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CONTRIBUTIONS 


CESTEffllAl  EXHIBITION. 


JOHIf    ERIOSSOX,    LL.D. 


HONORARY    DOCTOR    OF    PHILOSOPHY   OF    THE    ROYAL    UNIVERSITY    OF    LUND;     MEMBER    OF    THE 

ROYAL    ACADEMY   OF    SCIENCES,    STOCKHOLM;    MEMBER    OF    THE    ROYAL    ACADEMY   OF 

MILITARY  SCIENCES  OF  SWEDEN;    HONORARY  MEMBER  OF  THE  ROYAL  SCIENTIFIC 

SOCIETY  OF   UPSALA;    AND  MEMBER    OF    VARIOUS    OTHER    SCIENTIFIC 

INSTITUTIONS    IN    EUROPE    AND    AMERICA; 

KNIGHT    COMMANDER,    WITH    THE    GRAND    CROSS.    OF    THE    ORDER    OF    NORDSTJERNAN  ;    KNIGHT 

COMMANDER  OF   DANNEBROC,   FIRST  CLASS;    KNIGHT  COMMANDER  OF  ISABEL  LA 

CATOLICA;    KNIGHT   COMMANDER  OF    SANCT   OLAF ;    AND 

KKIGHT  OF  THE  ORDER  OF  VASA. 


NEW  YORK: 
PRmXED  FOR  THE  AUTHOR  AT   "THE  NATION"  PRESS. 


1876. 


INTRODUCTION. 


The  Commissioners  of  the  Ceuteunial  Exliil^itiou  baviug 
omitted  to  invite  me  to  exhibit  the  results  of  my  labors 
connected  with  mechanics  and  physics,  a  gap  in  their  re- 
cord of  material  progress  exceeding  one-third  of  a  century 
has  been  occasioned.  I  have  therefore  deemed  it  proper 
to  publish  a  statement  of  my  principal  labors  during  the 
last  third  of  the  century,  tlie  achievements  of  Avhich  the 
promoters  of  the  Centennial  Exhibition  have  called  upon 
the   civilized   world    to    recognize. 

The  nature  of  the  labors  referred  to  will  be  seen  by 
the  following  account  of  philosophical  instruments,  engines, 
and  other  structures  described  and  illustrated  in  this  work 
— viz.  :  Apparatus  for  measuring  the  intensity  of  radiant 
heat  at  given  distances.  Instrument  for  measuring  radiant 
heat  emitted  by  concave  spherical  radiators  within  exhausted 


^ 


iv  INTRODUCTION. 

euclosiires.  Instriimeut  showing  the  rate  of  cooling  of  a 
heated  body  within  an  exhausted  cold  enclosure.  Instru- 
ment showing  the  rate  of  heating  of  a  cold  body  ^vithi^ 
an  exhausted  heated  enclosure.  Instrument  showing  the  rate 
of  cooling  of  an  incandescent  sphere  within  an  exhausted 
cold  enclosure.  Instrument  for  measuring  the  dynamic 
energy  developed  by  radiant  heat  at  different  intensities. 
Actinometer,  for  measuring  the  temperature  developed  by 
solar  radiation.  Solar  Calorimeter,  for  measuring  the  dyna 
mic  energy  developed  by  solar  radiation.  Portable  Solar 
Calorimeter.  Parallactic  mechanism,  for  measuring  the  in 
tensity  of  radiation  from  different  parts  of  the  solar  disc 
Instrument  for  measuring  the  radiant  power  of  the  solar 
envelope.  Instrument  for  measuring  the  actual  intensity  of 
the  sun's  rays.  Solar  Pyrometer,  for  measuring  the  tempe 
rature  of  the  solar  sui'face.  Apparatus  for  measuring  the 
radiant  intensity  of  flames.  Instrument  fo]-  measuring  radi- 
ation from  incandescent  planes  at  different  angles.  Instru- 
ment for  measuring  the  radiation  from  different  zones  of 
incandescent  spheres.  Calorimeter,  for  measuring  the  dyna- 
mic enei'gy  developed  by  radiation  from  fused  iron.  Appa- 
ratus for  measuring  radiant  heat  by  means  of  the  thermo- 
electric pile.  Barometric  Actinometer,  for  measuring  the 
temperature  developed  by  solar  radiation.  Apj^aratus  for 
ascertaining  the  conductivity  of  mercury.     Concave  spherical 


INTRODUCTION.  t 

radiator,  for  testiug  the  accuracy  of  the  sohar  pyrometer, 
lustrumeut  for  measuring  the  reflective  power  of  silver  aud 
other  metals.  Rapid-indication  Actinometer,  for  measuring 
the  temperature  developed  by  solar  radiation.  Apparatus 
for  ascertaining  the  diathermancy  of  flames.  Dynamic  Re- 
gistei',  for  measuring  the  relative  power  of  currents  of  water 
and  vapor.  Distance-instrument,  for  measuring  distances 
at  sea.  Steam  fire-engine,  designed  1841.  Engines  of  the 
United  States  steamship  Princeton,  built  at  Philadelphia, 
1842.  Twelve-inch  wrought-iron  gun  aud  carriage  mounted 
on  board  the  Princeton,  1843.  Iron-clad  cupola  vessel,  de- 
signed 1854.  Surface-condenser  for  marine  engines,  patented 
1849,  built  at  New  York.  Experimental  caloric  engine, 
i)uilt  at  New  York,  1851.  Caloric  engine  for  domestic 
purposes,  extensively  introduced  in  Europe  and  America. 
The  iron-clad  turret-vessel  Monitor,  built  at  New  York, 
1861.  Turret-vessels  of  the  Passaic  class,  built  at  New 
York  and  other  places,  18G2.  The  Monitor  engine,  applied 
to  the  entire  iron-clad  fleet  of  the  United  States  during-  the 
war.  The  turret-vessel  Dictator,  built  at  New  York,  18G2. 
Carriages  for  heavy  ordnance,  designed  1861,  built  at 
numerous  mechanical  establishments  in  the  United  States. 
Pivot-carriages  of  the  Si"»anish  gunboats,  Imilt  at  New  York, 
1869.  Rotary  gun-carriage  and  transit  platform,  built  at 
New  York,   1873.     Gun-cai'riage  for  coast  defence,  designed 


Ti  INTRODUCTION. 

1861,  built  at  New  York.  ludepeudent  twin  sorew-engiues 
t)f  the  thirty  Spanish  gunboats,  built  at  New  York,  1869. 
New  system  of  naval  attack,  published  1870.  Movable  tor- 
pedo, biailt  at  New  York,  1873.  Air-compressor  for  the 
transmission  of  mechanical  poAver,  built  at  New  York,  1873. 
Solar  engine,  actuated  by  the  intervention  of  steam,  built 
at  New  York,  1870.  Solar  engine,  actuated  by  the  inter- 
vention of  atmospheric  air,  built  at  New  York,  1872. 

The  foregoing,  it  should  be  observed,  relates  to  work 
carried  out  by  me  on  American  soil.  It  has  no  reference 
to  my  labors  in  England  from  1826  to  1839  connected  with 
locomotion,  steam  navigation,  motive  engines,  and  other 
branches  of  mechanical  and  civil  engineering.  Nor  does  it 
contain  a  comj^lete  enumeration  of  the  original  mechanical 
inventions  carried  into  practice  by  me  in  the  United  States 
— models  of  which  would  have  been  presented  at  the  Cen- 
tennial Exhibition  had  its  promoters  desired  me  to  furnish 
a  record  of  my  share  in  the  progress  of  mechanical  engi- 
neering during  the  last  thirty-seven  years  of  the  first  cen- 
tury of  the  Kepublic. 

As  our  space  only  admits  of  a  brief  reference  to  the 
mechanical  inventions  adverted  to  and  not  described  or  illus- 
trated in  this  work,  the  following  statement  is  appended, 
furnishing  an  outline  of  the  principal  structures  omitted — 
viz. :  Engines  of  the  twin-screw  steamship  Clarion,  built  at 


INTIWDUVTION.  Tii 

New  York,  1S40,  cousistiug  of  two  vertical  cylinders,  placed 
fore  and  uft  iu  the  vessel,  actuating  tLe  cranks  of  the 
screw-shafts  by  inclined  conuectinof-rods.  Vertical  single 
engines,  actuating  twin  screws,  built  at  New  York,  1842, 
applied  to  sev^eral  freight  vessels  on  the  Delawai-e  and 
Knritan    Canal.     Single    horizontal    back-action    engine,    l)uilt 

1843,  applied  to  the  United  States  screw-steamer  Legare. 
Inclined  screw-engines,  built  1843,  applied  to  the  steam- 
ship Massachusetts,  the  steam-cylinders  of  which  weie 
placed  near  the  deck  at  the  ship's  sides,  secured  to  dia- 
gonal timbers  bolted  to  the  planking.  Centrifugal  suction- 
fan,  built  1843,  operated  by  an  independent  engine,  for 
producing  draught  in  marine  boilers  by  drawing  the  air 
through  the  furnaces  and  flues,  and  forcing  the  products 
of    combustion   into   the   chimney.      Inclined    engines,    built 

1844,  applied  to  the  bark  Edith,  the  connecting-rods  ope- 
rating at  right  angles  to  each  other  and  coupled  to  a 
common  crank-pin  on  the  piopeller-shaft.  Vertical  engines, 
built  1844,  applied  to  the  twin-screw  vessel  Midas  (the 
fii-st  screw-vessel  to  round  the  Cape  of  Good  Hope),  the 
power  being  transmitted  to  the  propeller-shafts  by  vertical 
connecting-rods  actuated  by  horizontal  beams  placed  trans- 
versely under  the  deck.  Vertical  engines  applied  to  nume- 
rous screw-vessels  employed  on  the  coast  and  inland  waters 
of    the   United   States,   the   cylinders    being   placed   perpen- 


viii  INTR  OB  UCTION. 

dicularly  above  the  propeller-shaft,  the  connecting-rods  act- 
ing downwards — a  form  of  engine  now  employed  in  nearly 
all  sea-going  steamers,  but  at  that  time  (about  1844) 
severely  criticised  by  marine  engineers.  Engines  of  the 
twin-screw  ship  Marmora,  built  1843,  consisting  of  vertical 
steam-cylinders  which,  by  means  of  beams  working  under 
the  deck  and  vertical  connecting-rods,  imparted  indepen- 
dent motion  to  the  pi'opeller-shafts.  Horizontal  high-pres- 
sure and  condensing  engine  of  the  twin-screw  steam-tug  R. 
B.  Foi'hes,  built  1844,  provided  with  detached  condenser 
and  air-pump  actuated  by  an  independent  engine — a  vessel 
which,  during  a  series  of  years,  rendered  valuable  service 
on  the  coast  of  Massachusetts  by  towing  and  relieving 
ships  in  distress.  Compound  stationary  engine,  actuated  by 
very  high  pressure,  in  which  the  steam  was  expanded  to 
the  utmost  extent,  elaborately  described  by  Dr.  Lardner, 
who  devoted  much  time  to  its  theoretical  consideration. 
Horizontal  engine  applied  to  the  screw-vessel  Primero,  actu- 
ated by  a  mixture  of  steam  and  atmospheric  air.  Stationary 
engines  actuated  by  highly  superheated  steam,  the  pistons  of 
which  were  single-acting  and  thoroughly  protected  against 
the  injurious  effect  of  high  temperature.  Experimental 
street-car,  propelled  by  a  doul^le  caloric  engine.  Hoisting 
machines,  actuated  by  cold  compressed  air,  applied  to  several 
warehouses  in  New  York.     Small  motors,   actuated  by  cold 


INTRODUCTION.  ix 

compressed  air,  successfully  applied  to  the  sewing-machines 
of  a  large  establishment  in  New  York,  intended  to  estab- 
lish the  fact  that  the  present  injurious  physical  exertion  of 
sewing-women  may  economically  be  dispensed  with. 

Regarding  the  descriptions  and  illustrations  of  the  caloi'ic 
engines  contained  in  this  work,  it  is  proper  to  observe  that 
they  relate  only  to  some  of  the  engines  which  I  have  built, 
at  least  ten  different  types,  unlike  those  described,  having 
been  constructed  and  practically  tested.  Nor  have  I  yet 
wholly  suspended  the  labors  connected  with  this  safe  and 
economical  engine.  The  fact  that  it  requires  no  water,  and 
that  its  principle  is  not  incompatible  with  the  desirable 
emplo}Tnent  of  very  high  temperature — apart  from  the  im- 
portant circumstance  that  the  use  of  atmospheric  air  admits 
of  returning  at  each  stroke,  by  the  process  of  regeneration, 
the  heat  not  converted  into  mechanical  work  during  the 
previous  movement  of  the  working  piston — justify  continued 
endeavors  to  perfect  this  remarkable  motor. 

J.    Ericsson. 

New  Yokk,  September,  1876. 


CONTENTS. 


CHAPTER  PAGE 

I. — Transmission  of  Radiant  Heat,    ....  1 

II. — Radiation  at  Different  Temperatures,     .        .  17 

III. — Intensity  of  Solar  Radiation,     ....  52 
IV. — Periodic  Variation  of  the  Intensity  of  Solar 

Radiation, 75 

v.— Mechanical  Energy  of  Solar  Radiation,          .  91 
VI. — Thermal  Energy  transmitted  to  the  Earth  by 
Radiation    from    Different    Parts   of   the 

Solar  Surface, 107 

VII.— The  Source  of  Solar  Energy,       ....  137 
VIII.— Radiating    Power    and    Depth    of   the   Solar 

Atmosphere, 153 

IX.— The   Feebleness   of   Solar    Radiation   demon- 
strated,           1^^ 


CONTENTS. 


CHAPTEE 

X. — Temperature  of  the  Solar  Surface, 
XL — Radiation  from  Incandescent  Planes,    . 
XII. — Eadiation  from  Incandescent  Spheres,  . 
XIII. — Radiation  from  Fused  Iron, 
XIV. ^ — Radiant  Heat  measured  by  the  Thermo-Elec 

TRic  Method, 

XV. — The  Thermoheliometer,        .... 
XVI. — Barometric  Actinometer,    .... 
XVII. — Conductivity  of  Mercury,  .... 
XVIII. — Incandescent  Concave  Spherical  Radiator, 
XIX. — Reflective    Power    of    Silver    and    other 

Metals, 

XX. — Rapid-indication  Actinometer 

XXI. — Solar  Radiation  and  Diathermancy  of  Flames, 
XXII. — Constancy  of  Rotation  of  the  Earth  incom- 
patible with  Solar  Influence,    . 
XXIII. — Distance    Instrument,    for    measuring    Dis- 
tances at  Sea, 

XXIV. — The  Steam  Fire-Engine, 

XXV. — The  Steamship  Princeton, 

XXVI. — Twelve-inch    Wrought-iron    Gun    and    Car- 
riage,          


FAQE 
181 

209 
220 
229 

239 
254 
266 
275 

285 

294 
310 
317 

327 

380 
386 
391 

400 


OONTENTa.  xiii 

CEAPTES  PAGE 

XXVII.— Application  of  the  Submerged  Propeller 

FOR  Commercial  Purposes,      .        .        .      404 
XXVIII. — Iron-clad  Steam  Battery,  with  Revolving 
Cupola,   submitted  to  Emperor  Napo- 
leon III., 410 

XXIX. — Surface-Condenser,  operated  by  Indepen- 
dent Steam  Power, 417 

XXX.— The     Caloric     Engine  —  Application    of 

Heated  Air  as  a  Motor,         .        .        .      425 
XXXI.— Caloric  Engine  for  Domestic  Purposes,  .      439 
XXXII.— The  Monitor  System  of  Iron-clads,   .        .      460 
XXXin. — The  Monitor  Turret  and  the  Centennial 

Exhibition, 471 


XXXIV.— The  Monitor  Engine, 478 

XXXV.— The  Monitor  Dictator,          ....  492 

XXXVI.— The  Monitor  Turret  and  the  Casemate,  .  498 

XXXVII.— Carriages  for  Heavy  Ordnance,        .        .  505 
XXXVIII.— Pivot  Carriages  of  the  Thirty  Spanish 

Gunboats, 510 

XXXIX.— Rotary  Gun-Carriage  and  Transit  Plat- 
form,      517 

XL.— Gun-Carriage  for  Coast  Defence,     .        .  521 


xiv  CONTENTS. 

CHAJTEB  PAOB 

XLI.— The    Thirty    Spanish    Gunboats    and    their 

Engines, 625 

XLII. — A  New  System  op  Naval  Attack,      .        .        .  632 
XLIII. — Submarine  Warfare — The  Movable  Torpedo,  540 
XLTTV". — Transmission  of  Mechanical  Power  by  Com- 
pressed Air, 549 

XLV.— Sun  Power— The  Solar  Engine,         .        .        .  568 


LIST   OF   PLATES. 


PLATX 

1.  Apparatus  for  measttring  Radiant  Heat. 

2.  Instrument  for  measuring  the  Intensity  ok  Radiation 

FROM  Enclosed  Concave  Radiators. 

3.  Diagrams  showing  the  Propagation  of  Radiant  Heat 

THROUGH  Space. 

4.  Instrument  showing  the  Rate  of  Cooling  of  a  Heated 

Body  within  an  Exhausted  Cold  Enclosure. 
6.   Instrument  showing  the  Rate  of  Heating  of  a  Cold 
Body'  within  an  Exhausted  Heated  Enclosure. 

6.  Instrument  showing  the  Rate  of  Cooling  of  an  Incan- 

descent Sphere   within  an  Exhausted  Cold  Enclo- 
sure. 

7.  Instrument  for  measuring  the  Dynaiuo  Energy  deve- 

loped BY  Radiant  Heat. 


XVI  LIST  OF  PLATES. 

PLATE 

8.  actinometer   for   measuring  the  intensity   oe  solak 

Radiation. 

9.  Diagrams   showing  the  Intensity  of  Solar  Radiation 

AT  Different  Zenith  Distances. 

10.  Solar    Calorimeter,    for    measuring   the    Mechanical 

Energy  of  Solar  Radiation. 

11.  Portable   Solar  Calorimeter,  for  measuring  the  Me- 

chanical Energy  of  Solar  Radiation. 

12.  Diagrams  showing  the  Radiation  from  Different  Parts 

of  the  Solar  Disc. 

13.  Parallactic  Mechanism  for  measuring  the  Intensity  of 

Radiation  from  Different  Parts  of  the  Solar  Disc. 

14.  Diagram    showing    the    Attraction   within   the    Solar 

Mass  at  Different  Distances  from  its  Centre. 

15.  Instrument  for  measuring  the  Radiant  Power  of  the 

Solar  Atmosphere. 

16.  Diagrams  showing  the  Radiant  Power  of  the  Solar 

Atmosphere. 

17.  Instrument   for   measuring   the   Actual   Intensity   of 

the  Sun's  Rays. 

18.  Instrument  for  showing  the  Feebleness  of  Solar  Ra- 

diation. 


LIST  OF  PLATES.  xvii 

PLATE 

19.  Solar  Pyrometer,  for  ascertainiis^g  the  Temperature 

OF  the  Solar  Surface. 

20.  Apparatus   for   measuring   the  Radiant  Intensity  of 

Flames. 

21.  Instrument  for  measuring  the  Radiation  from  Incan- 

descent Planes. 

22.  Diagrams  showing  the  Radiation  at  Different  Incli- 

nations OF  Incandescent  Planes. 

23.  Instrument  for  measuring  the  Radiation  from  Diffe- 

rent Zones  of  Incandescent  Spheres. 

24.  Diagrams  showing  the  Radiation  from  Different  Zones 

OF  Incandescent  Spheres. 

25.  Calorimeter,  for  measuring  the  Energy  developed  by' 

Radiation  of  Fused  Iron. 
2G.   Appar.vius  for  measuring  Radiant  Heat  by  Means  of 
the  Thermo-Electric  Pile. 

27.  Barometric  Actinomf.ter,  for  sieasuring  the  Intensity 

OF  Solar  Radiation. 

28.  Apparatus  for  ascertaining  the  Conductivity  of  Mer- 

cury. 

29.  Concave  Spherical  Radiator,  for  testing  the  Accuracy 

of  the  Solar  Pyrometer. 


xviii  LIST  OF  PLATES. 

PLATE 

30.  Instrument  for  measuring  the  Reflective  Power  of 

Silver  and  other  Metals. 

31.  Rapid-indication  Actinometer,  for  measurinc+  the  In- 

tensity OF  Solar  Radiation. 

32.  Apparatus    for   ascertaining    the    Diathermancy    of 

Flames. 

33.  Diagram  representing  a  Section  of  the  Earth  and  cer- 

tain River  Basins. 

34.  Dynamic  Register  for  measuring  the  Relatia'e  Power 

OF  Currents  of  Water  and  Vapor. 

35.  Diagram  showing  the  Result  of  Experiments  with  the 

Dynamic  Register. 

36.  Distance  Instrument,  for  measuring  Distances  at  Sea. 

37.  Steam  Fire-Enchne. 

38.  Engines  of  the  "  Princeton"— Transverse  Section  of 

Semi-Cylinders  and  Piston. 

39.  Engines  of  the  "  Princeton  "—Front  Elevation. 

40.  Engines  of  the  "  Princeton"— Elevation  vieaved  from 

the  Stern. 

41.  Twelve-inch  Wrought-iron  Gun  and  Carriage. 

42.  Iron-clad  Cupola  Vessel— Side  Elevation  and  Trans- 

verse Section. 


LIST  OF  PLATES.  xix 

PLATE 

43.  Sl'RFACE   COXDF.XSER. 

44.  Experimental  Calokic  Exgine— Traxsverse  Section. 
4,").   Experimental  Caloric  Exgixe— Loxcitudixal  Sectiox. 
4G.   Caloric  Exgixe  for  Domestic  Purposes— Loxgitudixal 

Section. 

47.  The    "  Moxitor"— Side    Elevation,    Deck    Plan,    and 

Transverse  Sectiox  of  Hull  and  Turret. 

48.  MoxiTOR  "  Weeiiawken  "   AT  Sea. 

49.  MoxiTOR    OF   THE     "  Passaic  "     Class  —  Side   Elevattox 

AXD    Tkaxsverse    Sectiox    of    Turret    and    Pilot- 
house. 
!)0.    The  Moxitor  Exgixe — Top  View. 

51.  The  Monitor  Exgixe — Front  Elevation. 

52.  Monitor  "Dictator"— Side  Elevation  axd  Deck  Plax. 

53.  Monitor  "  Dictator"— Traxsverse  Section  of  Exgixes 

AXD  Ship. 

54.  Moxitor  "Dictator" — Top  View  of  Engines. 

5.'").   Monitor    ••  Dictator"    on    the    Stocks,    prepared    for 

Launching. 
56.   The  Monitor  Turret  and  the  Casemate — Deck  Plan  of 

A    ^^OXITOR    WITH    Two    TURRETS — Df.CK     PlAX    OF    THE 

Turkish  Irox-clad  "Moyixi  Zaffir." 


XX  LIST  OF  PLATES. 

PLATE 

57.  CaeeiaCtES  foe  Heavy  Oednanoe — Section  showing  the 
Feiction  Geae  applied  to  the  Gun-Caeeiages  of  the 
United  States  Ieon-Clad  Fleet — Section  showing 
Captain  Scott's  Plagiaeism — Section  showing  Sie 
William  Aemsteong's  Plagiaeism. 

SS.   Pivot  Caeeiage  of  the  Spanish  Gunboats. 

59.  Rotaey   Gun-Caeeiage  and  Teansit  Platfoem  applifj) 

to  the  Spanish  Gunboat  "  Toenado." 

60.  Gun-Caeeiage  foe  Coast  Defence. 

61.  The  Spanish  Gunboat  Engines. 

62.  A  New  System  of  Naval  Attack. 

63.  Movable  Toepedo. 

64.  Aie-Compressoe,   foe  the  Transmission  of  Mechanical 

Power — Perspective  View. 

65.  AlE-COMPRESSOR,    FOE    THE    TeANSMISSION    OF    MECHANICAL 

Power — Teansverse  Section. 

66.  Solar  Engine,  operated  by  the  Inteevention  of  Steam. 

67.  SoLAE  Engine,  opeeated  by  the  Inteevention  of  Atmo- 

spheric Air. 


CHAPTER    I. 

TRANSMISSION   OF   RADIANT   HEAT. 


No  phenomenon  connected  with  radiant  heat  supposed  to 
have  been  thoroughly  investigated  is  so  imperfectly  under- 
stood as  its  propagation  through  space.  The  recognized  doc- 
trine, which  asserts  that  the  temperature  imparted  to  substances 
exposed  to  radiant  heat  diminishes  in  the  inverse  ratio  of  the 
square  of  the  distance  from  the  radiating  body,  is  true  only 
of  a  sphere  of  perfectly  uniform  temperature  at  the  surface,  if 
the  distance  be  computed  from  the  centre  of  the  sjihere.  The 
temperatui-e  produced  by  radiation  of  spheres  which  ai'e  not 
uniformly  heated  at  all  points  of  their  surface,  and  of  other 
bodies  of  whatever  form,  we  have  no  exact  means  of  ascertain- 
ing, although  the  distance  and  the  temperature  of  the  radiating 
body  be  accurately  known.  Nor  will  it  avail  if,  in  addition 
to  the  assumed  known  uniform  tempei-ature  and  accurate 
knowledge  of  distance,  we  also  know  the  dimensions  of  the 
radiator.  In  fine,  notwithstanding  our  knowledge  of  these 
elements,  an  attempt  to  solve  the  problem  will   be  fruitless, 


2  L'ADTAXT  HEAT.  chap.  I. 

unless,  as  before  stated,  the  radiation  i^'oeeeds  from  a  }<phere 
of  known  diameter  having  a  imiform  temperature  at  its  suii'ace. 
According  to  Melloui's  theory,  which  Pi'ofe.ssor  Tyndall  and 
sOme  eminent  French  scientists  assure  us  has  been  unanswer- 
ably demonstrated  l)y  the  celebrated  Italian,  the  matter  is 
very  simple,  namely:  the  temperature  at  intermediate  points 
between  a  heated  body  and  a  thermometer  placed  at  a  o-iven 
distance,  exposed  to,  and  indicating  the  intensity  of  the  radiant 
heat,  may  be  determined  by  squaring  the  respective  distances 
from  the  radiator.  The  products,  it  is  asserted,  will  show  the 
inverse  ratio  of  the  intensities,  and  consequently  the  tempera- 
ture at  the  intermediate  points,  due  to  their  distance  from 
the  radiating  sni-face.  The  question  being  of  great  practical 
importance,  I  have  examined  the  merits  of  Melloni's  mode 
of  establishing  the  infalliljility  of  the  propounded  doctrine 
that  the  temjiei'ature  inq)arted  to  bodies  exposed  to  radiant 
heat  are  in  the  inverse  ratio  of  the  distances  between  the 
radiating  surface  and  those  bodies.  The  illustration  shown 
on  the  first  plate  represents  an  apparatus  constructed  for  the 
purpose  of  testing  practically  whethei'  the  exjieriment  referred 
to  by  Professor  Tyndall  in  "  Heat  as  a  Mode  of  Motion  "  really 
fui-nishes  positive  evidence  of  the  correctness  of  Melloni's 
theory  accepted  by  the  distinguished  experimentalist  and  ])y 
certain  Fi'ench  authors,  a  represents  the  section  of  a  rect- 
angular vessel  filled  with  hot  water,  the  face  g  h  being  coated 
with  lamp-black.  A  hollow  cone  c,  lined  with  black  paper 
on  the  inside,  is  secured  to  a  thermo-electric  pile  c',  supported 
by  an  appropriate  stand  sliding  in   a  groove  formed   at   tlie 


CHAP.  1.  TL'A.XS.yiSt^IOX  Of  n.llHAXT  IfKAT.  3 

to[)  of,  and  iiarallel  with,  the  ceiitie  Hue  of  the  table  on  Avliicli 
the  apparatus  is  placed.  It  will  be  evident  that  this  airaiit^e- 
ment  prevents  any  change  of  direction  of  the  axis  of  the  cone 
which  should  be  right  angular  to  the  heated  vessel,  during 
the  movement  of  the  pile.  Melloni  asserts  that  if  the  cone 
c  be  moved  towards  the  heated  vessel,  say  to  the  position  b, 
the  needle  of  the  galvanometer  connected  with  the  i)ile  will 
remain  stationary.  His  accepted  reasoning  defining  the  law 
which  governs  the  transmission  of  radiant  heat  being  based 
solely  on  the  correctness  of  this  assumption,  I  have  carried 
out  an  elaborate  series  of  experiments  to  ascertain  if  the 
needle  of  the  galvanometer  remains  absolutely  stationary  as 
shown  by  Prof.  Tyndall  dui'ing  the  exhibitions  at  the  Royal 
Institution,  mentioned  in  his  work  on  heat  before  alluded 
to.  The  result  establishes  the  fact  most  positively  that  the 
needle  does  not  remain  stationary  as  assumed,  and  that  the 
deflection  \\hich  takes  place  increases  considerably  as  the  pile 
is  advanced  towards  the  heated  vessel.  That  such  should  be 
the  case  will  be  evident  on  due  reflection.  A  careful  inspec- 
tion of  the  diagram  shows  that,  because  the  points  ;/  and  d 
of  the  i-adiating  surface  are  not  equidistant  from  c',  the  i-adiant 
heat  which  they  emit  cannot  affect  the  face  of  the  pile  alike. 
The  extent  of  the  irregularity  may  be  approximately  deter- 
mined by  squaring  the  distances  g  c'  and  d  c'.  Now,  the  pro- 
portion of  these  distances,  as  shown  by  the  diagi-am,  is  20 
to  19,  hence  the  radiant  heat  transmitted  to  the  pile  from 
the  points  (/  and  d  will  vary  in  the  invei-se  ratio  of  the  pro- 
ducts of  the  stated  numbers,  viz.  :  as  3(51  to  400.     In  view  of 


4  FADIANT  HEAT.  CHAP.  I. 

this  great  diflference  of  intensity  of  the  heat  transmitted  to 
the  face  of  the  pile  from  different  points  of  the  radiating 
surface,  the  readers  of  "  Heat  as  a  Mode  of  Motion  "  may  with 
propriety  ask  if  the  intensity  indicated  by  the  galvanometer 
connected  with  the  thermo-electric  pile  during  the  reported 
experiments  at  the  Eoyal  Institution  was  that  due  to  the 
radiant  heat  transmitted  from  g  in  the  line  of  g  c',  or  that 
transmitted  from  d  along  d  c'. 

On  theoretical  grounds,  therefore,  Melloni's  demonstration 
is  quite  unsatisfactory.  Several  imperfections  of  a  practical 
nature,  insej^arable  from  the  method  adopted  by  the  Italian 
physicist,  demand  consideration,  all  tending  to  aggravate  the 
theoretical  defects.  The  black  paper  which  lines  the  inside 
of  the  hollow  cone  h,  being  very  light  and  incapable  of  reflect- 
ing the  radiant  energy  transmitted  by  the  heat-rays  1c  r  and  m 
0,  will  at  once  become  heated,  consequently  the  air  contained 
within  the  cone  will  speedily  have  its  temperature  raised  by 
convection.  The  heat  thus  received  will  radiate  towards  the 
face  of  the  pile  and  thereby  contribute  to  disturb  the  indi- 
cation, already  seriously  affected  by  the  difference  of  tempe- 
rature consequent  on  the  varying  intensities  of  the  radiant 
heat  transmitted.  The  relative  intensity  imparted  to  the  black 
paper  within  the  cone  h,  and  that  transmitted  to  the  pile  b', 
may  be  ascertained  by  squaring  the  length  of  the  heat-rays 
d  0  and  d  h'.  The  diagram  shows  that  these  lengths  are  as 
3  to  5  ;  hence,  by  squaring  and  inversion,  we  find  that  the 
temperatui'e  imparted  by  the  radiant  heat  at  o  will  be  greater 
than  that  at  b'  in  the  proportion   of  25  to  9.     Black  pajjer 


(UAp.  I.  TI!ANS^^ssI()^^  of  l-adtant  heat.  5 

being  a  powei-ful  radiator,  wbile  air  has  ver\  small  specific 
heat,  it  will  be  perceived  that  the  volume  within  the  cone 
will  rapidly  become  heated  by  convection,  as  already  stated, 
and  therefore  the  temperatui'e  of  the  face  of  the  pile  will  be 
elevated  to  a  degree  far  beyond  that  Avhich  it  would  attain 
by  the  direct  radiation  of  the  vessel  a.  Before  presenting 
a  demonstration  2>roving  the  fallacy  of  Melloni's  assertion, 
that  the  temperatures  imparted  to  bodies  exposed  to  radiant 
heat  are  "  iuverseli/  rt6'  (he  square  of  the  distances  hi-txveett,  tlie 
radiating  Sfiirface  and  those  bodies,'^  I  propose  to  give  a  de- 
tailed statement  of  the  elaborate  experiments  before  adverted 
to,  instituted  for  the  purpose  ctf  showing  practicaUij  that  the 
assertion  which  forms  the  basis  of  the  accepted  doctrine  is 
false,  and  that  the  hollow  cone  c  cannot  be  moved  to  the 
position  h  without  increasing  the  deflection  of  the  needle  of 
the  galvanometer  connected  with  the  theniio-pile.  It  has 
already  been  stated  that,  in  order  to  insure  pei-fect  parallel- 
ism during  the  movement,  the  stand  which  supports  the  cone 
and  pile  slides  in  a  groove  parallel  with  the  table  on  which 
the  radiating  vessel  a  is  placed,  and  at  right  angles  to  the 
face  of  the  latter.  A  scale  h,  divided  into  inches,  is  attached 
to  the  side  of  the  table  for  the  purpose  of  showing  the  distance 
between  the  pile  and  the  vessel  a,  the  face  of  the  latter  coin- 
ciding Avith  the  zero  of  the  scale.  The  mode  of  conducting 
the  experiment  will  be  seen  by  the  following  brief  explanation. 
The  hollow  cone  c  was  placed  so  that  the  vertical  line  of  the 
face  d  corresponded  with  the  last  division  of  the  scale,  a  screen 
being  introduced  for  the  i>urpose  of  shutting  off  the  radiation 


6  BADIANT  HEAT.  CHAP.  I. 

from  the  blackened  face  of  tlie  vessel  a.  Maintaining  the  water 
in  the  latter  at  a  constant  tenaperatnre  of  130°  above  that  of 
the  surrounding  atmosphere,  it  Avas  found  on  removing  the 
screen  that  the  needle  of  the  galvanometer  moved  4.7  deg. 
from  zero  during  an  intel•^'al  of  30  seconds  from  the  moment 
of  exposing  the  face  of  the  pile  to  the  radiator.  The  vessel 
a  was  then  I'emoved  and  carried  into  an  adjoining  room  to 
allow  the  pile  to  cool  while  thus  thoroiighly  protected  from 
the  radiation  of  the  heated  vessel.  In  the  meantime,  a  spirit- 
lamp  was  applied  under  the  vessel  in  order  to  make  good 
the  heat  lost  during  the  preceding  operation.  Sufficient  time 
having  elapsed  to  allow  the  pile  to  cool,  the  vessel  was  again 
put  in  position  on  the  table.  The  pile  being  then  advanced 
to  the  10th  division,  and  the  screen  withdrawn,  the  needle 
moved  5.05  deg.  from  zero  in  the  same  time  as  before,  viz., 
30  seconds.  The  vessel  was  removed  a  third  time  into  the 
adjoining  room,  the  tempei'ature  raised  to  the  fixed  point, 
the  pile  allowed  to  cool,  and  the  vessel  placed  in  position  as 
before.  The  pile  being  now  advanced  to  the  5th  division 
on  the  scale,  and  the  screen  raised,  the  needle  moved  5.55 
deg.  from  zero  in  the  stipulated  time  of  30  seconds.  It  will 
be  seen  then  that,  so  far  from  remaining  stationary,  the  deflec- 
tion of  the  needle  of  the  galvanometer  increases  very  con- 
siderably as  the  pile  is  advanced  towards  the  radiator.  The 
important  fact  remains  to  be  noticed,  that  the  needle  conti- 
nues to  move  rapidly  after  the  expiration  of  30  seconds  from 
the  time  of  exposing  the  pile  to  the  radiator ;  a  circumstance 
furnishing  additional  evidence  of  the  unsatisfactory  nature  of 


TL'AM>MJSt^I<>.\  (>/•  A'.( /»/.!. VV  HEAT. 


Melloui's  methoil.  In  tuder  to  asceitaiii  the  exact  extent  uf 
deflection  of  the  needle,  referred  to,  two  distinct  sets  of  expe- 
riments were  made,  the  mean  result  of  which  is  exhibited  in 
the  accompanying  table.     The  position  of  the  needle  of  the 


Distance  axd  Deflection. 

Time. 

1 

20  ins. 

10  ins. 

5  ins. 

Stcond). 

I>tg. 

Dv. 

D^. 

80 

4.70 

5.05 

5.55 

60 

4.80 

5.00 

6.75 

90 

4.r)0 

5.70 

8.25 

120 

4.7;-) 

6.25 

10.15 

galvanometer,  it  will  he  seen,  was  recoi'ded  at  the  expiration 
of  80,  60,  i>0,  and  120  seconds.  A  glance  at  the  table  proves 
the  correctness  of  the  objections  previously  raised  against  the 
detail  of  Melloni's  arrangement,  especially  the  distui'bing  influ- 
ence of  the  rays  projected  against  the  interior  of  the  cone 
from  points  fir-i/on//  the  ai'ea  whose  I'adiatioii  is  supposed  alone 
to  affect  the  pile.  Having  thus  practically  shown  the  fallacy 
of  the  assumption  on  j^hich  the  Italian  physicist  bases  his 
doctrine,  I  will  now  prove  its  unsoundness  by  the  i)rocess  f)f 
demonstration.  For  this  purpose  let  us  suppose  that  an  in- 
candescent cylindrical  block  I  (see  illustration  Plate  1)  com- 
posed of  cast  iron,  (1  inches  in  diameter,  be  suspended  at  such 
a  height  that  its  axis  passes  through  the  centre  of  the  bulb 
of  a  thermometei-  //i,  jield  by  a  bracket  in'  sliding,'  in  a  groove 


8  BADIANT  MEAT.  chap.  i. 

similar  to  that  formed  at  the  opposite  end  of  the  table,  before 
described.  A  scale  7i,  divided  into  equal  parts,  is  attached  to 
the  side  of  the  table,  the  zero  of  this  scale  coinciding  with 
the  vertical  line  drawn  from  the  face  of  the  incandescent  cylin- 
drical block  I ;  while  the  last  division  corresponds  with  the 
vertical  line  passing  through  the  centre  of  the  bulb  of  the 
thermometer  m.  Actual  trial  shows  that,  if  the  incandescent 
iron  block  be  suspended  while  its  temperature  is  1,200°,  the 
thermometer  exposed  to  its  radiant  heat  wall  indicate  22°  above 
that  of  the  surrounding  atmosphere  when  the  block  has  cooled 
so  far  that  its  differential  temperature  has  become  reduced  to 
1,000.°  Now,  agreeably  to  Melloni's  doctrine,  the  thermometer 
m,  if  advanced  to  the  10th  division  of  the  scale,  will  indicate 

20'  X  22 
a  differential  temperature  of  ; —  =  88° ;  if  advanced  to 

...        20'  X  22 

the  5th  division,  =  352° ;  if  further  advanced  to  the 

5' 

20'  X  22 
2d  division, ^ =  2,200° ;  and,  lastly,  if  advanced  to  the 

1st  division  on  the  scale,  the  thermometer  will   indicate   an 

20'  X  22 
intensity  of =  8,800°.  The  temperature  of  the  incan- 
descent radiating  block  being  only  1,000°,  Ave  have  thus  demon, 
strated  the  utter  fallacy  of  Melloni's  theory,  based  on  the  result 
of  imperfect  experiments  with  hollow  cones  and  thermopiles 
exposed  to  radiant  heat.  In  view  of  the  foregoing  facts  writers 
on  radiant  heat  will  do  well  to  expunge  this  eiToneous  theory 
from  their  works.  Practical  men,  not  suspecting  that  the  law 
of  inverse  squares  is  inapplicable  to  short  distances,  frequently 


CHAP.  I.  TL'Ays.VISSIoS  OF  I,'AniA.\T  HEAT.  9 

coiiiinit  serious  mustakes  in  ralculatiug  the  effect  of  phuiiii;' 
iiu-andescent  bodies  at  eeitain  distances  from  structures  in- 
tended to  be  heated.  But  Melloni's  device,  alt]iout,di  inca- 
pable of  elucidatin<f  the  principles  wliicli  govern  the  trans- 
mission of  radiant  heat,  possesses  great  value,  as  it  proves 
the  correctness  of  the  ai)parently  absurd  proposition,  that  an 
increase  of  the  surface  of  a  radiator  is  capa1)le  of  elevating 
the  temperature  of  a  substance  exposed  to  radiant  heat  with- 
out increasing  the  temperature  of  the  radiator.  The  import- 
ance of  this  fact  cannot  well  be  overstated.  It  contradicts 
ceitain  modem  sijeculations  regarding  radiant  heat,  and  it 
afl'ords  a  landmark  which,  tliough  it  does  not  point  out  what 
we  seek,  guards  against  taking  the  WToug  coui"se. 

The  defects  of  Melloni's  method,  and  its  inadequacy  to 
solve  the  problem  under  consideration,  suggest  the  question : 
Is  it  possible  to  determine,  by  calculation,  what  temperature 
sul)stances  will  acquire  by  being  placed  at  various  distances 
from  the  surface  of  a  heated  body  of  known  temperature  and 
dimensions,  the  sides  of  which  are  stiaight  and  parallel  (  "NVe 
are  compelled  to  admit  that  the  question  thus  presented  cannot 
be  satisfactorily  answered,  because  each  point  of  the  radiating 
surface,  in  consequence  of  varying  distance,  transmits  a  dif- 
ferent degree  of  intensity  to  the  exposed  substances.  The 
difficulty  of  solution  is  increased  on  account  of  the  stipulated 
form ;  the  inferior  intensity  transmitted  from  the  cornei-s  of 
the  radiator  rendering  the  question  exceedingly  complicated. 
A  radiating  plane  surface  of  circitlar  fonn  somewhat  simplifies 
the  (juestion;   yet  the  difficulty  remains  of  dealing  with  the 


10  RADIANT  HEAT.  chap.  i. 

inferior  power  of  the  heat-rays  euiauating  from  the  eirciuii- 
ference.  To  overcome  this  difficulty,  I  have  coustructed  au 
instrument — shown  Ijy  the  illustrations  on  Phite  2,  represent- 
ing a  longitudinal  section  and  a  perspective  view  (cojned 
from  a  photograph) — in  which  the  radiating  surface  is  con- 
cave, forming  part  of  a  sphere  whose  centre  is  situated  near 
the  centre  of  the  bulb  of  the  thermometer  employed  to  ascer- 
tain the  intensity  of  the  radiant  heat.  But  tliis  expedient  of 
employing  a  concave  spherical  surface,  every  point  of  which 
is  equidistant  from  the  bulb  of  the  thermometei',  prevents 
any  change  of  distance  between  the  same  and  the  radiator 
during  experiments.  I  have  accordingly  introduced  four  dis- 
tinct discs  of  varying  spherical  concavity,  with  a  thermometer 
placed  in  the  centre  of  curvature  of  eacli.  These  four  con- 
cave discs  forni  the  sides  of  an  open  vessel  filled  with  oil, 
heated  by  a  gas  flame.  In  order  to  facilitate  comparison,  a 
regular  gradation  of  curvature  has  been  adopted ;  the  radius 
of  the  deepest  concavity  being  3  in.,  the  next  being  6  in., 
then  9  in.,  and,  lastly,  12  in.  for  the  least  concavity.  It  will 
be  evident  that,  owing  to  the  difference  of  curvature,  each 
disc  mil  present  a  different  extent  of  radiating  surface,  if  a 
uniform  size  be  employed,  thereby  rendering  comparisons  be- 
tween the  indicated  intensities  quite  laborious.  To  obviate 
this,  the  diameters  of  the  several  discs  have  been  so  propor- 
tioned that  the  superficial  measurement  of  each  is  precisely 
alike.  The  disc  of  the  least  curvature  is  4  in.  in  diameter; 
the  remaining  three  being  respectively  3.982  in.,  3.939  in.,  and 
3.777   in.  diameter.      Much  pains  has  been  bestowed  on  the 


CHAP.  I.  TRAXSMISSloy  OF  EADrAXT  HEAT.  1] 

workmanship  in  order  to  obtain  concavities  of  precisely  equal 
ai-eas.  The  ulijection.s  raised  iu  subsequent  chapters  against 
conducting  experiments  with  the  solar  calorimeter  and  actiuo- 
iiictcr  in  the  presence  of  the  disturltiii^'  inlluence  of  the  sur- 
rounding air,  apply  witli  equal  force  to  the  apparatus  now 
being  considered.  Accordingly,  the  heater,  with  its  four  con- 
cave radiating  discs  and  thermometers,  are  enclosed  in  an 
exhausted  cliamber,  as  will  be  seen  by  reference  to  the  longi- 
tudinal section.  Evidently,  the  heat  reflected  by  the  sides  of 
this  chamber  towards  the  bulbs  of  the  enclosed  therniome- 
teis,  will  determine  their  zero  precisely  as  iu  the  instiuments 
referred  to;  hence,  it  is  indispensable  that  this  chamber  should 
be  maintained  at  a  constant  temperature.  This  is  effected  ])v 
surrounding  the  same  with  an  external  ojjeu  vessel  filled  with 
water  kept  at  a  tempei'ature  of  (50  deg.  Fahr.  during  experi- 
ments. The  object  of  adopting  60  deg.  is  that  of  facilitating 
comparisons  with  solar  intensity,  the  zero  of  my  actinometer 
being  also  (iO  deg.  above  Fahrenheit's  zero.  Let  us  now  con- 
sider briefly  the  leading  properties  of  the  illustrated  device. 
In  the  first  place,  the  radiating  concave  surfaces,  as  well  as 
the  liulbs  of  the  thermometeis,  are  surrounded  by  the  ether 
alone,  and  thei'efore  cannot  suffer  any  loss  of  heat  by  con- 
vection. SecDudly,  the  intensity  of  the  radiant  heat  received 
from  all  i)oints  of  each  concave  surface  will  be  precisely 
alike,  because  those  points  are  equidistant  from  their  respec- 
tive thermometers.  Thirdly,  the  concave  surfaces  presenting 
e(|ual  areas,  being  composed  of  the  same  materials  of  uiiilonu 
thickness,  and  beiuLf  heated  bv  the  same  medium,  will    emit 


12  JiADTAXT  HFAT.  CHAP.  I. 

an  eqiinl  amount  of  licat.  Fourtlily,  as  the  several  thei'nio- 
meters  are  exjioscd  to  tlie  radiation  of  a  surrounding  vessel 
kept  at  60  deg.,  they  ^vill  acquire  that  temperature  before 
fire  is  a})plied  to  the  heater.  In  consequence  of  this,  the 
increase  of  temperature,  after  heating,  will  furnish  a  ti-ue  com- 
parative measure  of  the  energy  of  the  radiant  heat  transmitted 
from  the  concave  radiators  to  tlie  bulbs  of  the  thennometers. 

The  prevailing  opinion  that  there  is  a  concentration  of  heat 
in  the  focus  of  spherical  radiators,  will  be  urged  as  an  objection 
against  the  described  method  of  measuring  radiant  heat.  A 
careful  examination  of  this  question  -svill  therefore  be  neces- 
sary. Fig.  4,  Plate  ?>,  represents  a  concave  spherical  radiator, 
0  being  the  focus,  o  c  the  axis,  and  a  h  a  section  of  the  I'adiator. 
According  to  the  accepted  theory  of  radiation,  rays  of  heat 
are  projected  in  all  directions  from  every  point  of  the  I'adiat- 
ing  surface.  In  order,  therefore,  to  demonstrate  that  there  is 
no  concentration  of  heat  in  the  focus,  we  have  merely  to  draw 
radial  lines  representing  the  heat-rays  from  points  d  and  /' 
on  the  concave  surface,  as  shown  on  the  diagram.  It  will 
be  seen  on  close  examination  that  there  is  only  a  single  ray 
d  c  emitted  from  the  point  d,  which  is  directed  towards  the 
focus  c ;  the  ray  /'  c  being  the  only  one  directed  from  the 
point/'.  The  other  heat-rays  from  the  points  d  and/'  diverge 
in  all  directions,  and  intersect  every  part  of  the  field  I'  1 ; 
thus  dispersing  the  radiant  heat  nearly  uniformly  over  a  very 
large  surface.  The  curve  c  >i,  struck  from  the  point  _/',  clearly 
shows  that  all  the  heat-i'ays  below  c,  projected  from  f,  are 
shoi'ter  than  those  dii'ected  to  the  forns  from  the  same  point, 


cnAP.  I.  TPA^'s^fTf!fi^o^'  of  i^adtaxt  heat.  13 

and  tlu'ivfore  impart  a  hiijJnr  tcinpciatiin-  to  the  plane  h  I 
than  that  transmitted  to  the  focus.  It  will  be  needless  to 
enter  on  a  detailed  computation  of  the  temperature  at  the 
intersections  of  the  vai'ious  I'ays  with  the  plane  h  1,  as  a 
mere  inspection  of  the  diagram  distinctly  shows  that  the 
focus  c  receives  no  increase  of  heat  on  account  of  being  the 
centre  of  the  spherical  radiator.  Indeed,  if  we  snl>stitute  a 
plane  circular  disc  extending  from  <i  to  /',  a  greater  amount 
of  heat  will  be  transmitted  to  a  thermometer  placed  at  <\ 
than  w  ith  the  spherical  surface  represented ;  the  only  impoi-- 
tant  difference  between  a  plane  and  a  concave  i-adiator  being 
that  a  thei'monieter  jilaced  in  the  focus  of  the  latter  receives 
an  equal  degree  of  heat  from  each  point  of  the  concave  surface. 
Investigations  conducted  by  means  of  tlie  illustrated  instni- 
nient  prove  that  the  intensity  of  heat  transmitted  by  the  radi- 
ation of  concave  spliciical  suii'aces  of  eipial  temperature,  pre- 
senting equal  areas  anil  having  ditt'ei'ent  curvature,  is  in  the 
inverse  ratio  of  the  square  of  their  ladii,  pi-ovided  the  sub- 
stance which  receives  the  radiant  heat  is  placed  in  the  focus 
of  the  radiating  sui'face.  This  impoitant  fact  in  coiiiiectiou 
with  the  jtrevious  demonstrations  showing  the  fallacy  of  the 
propounded  doctrine  that  the  intensity  of  ladiation  diminishes 
in  the  invei-se  ratio  of  the  square  of  the  distance,  between 
jdane  radiatoi-s  and  the  recijiients  of  their  radiant  heat,  enables 
us  now  to  consider  the  proposition  contained  in  our  inti-oduc- 
tory  remarks,  viz.,  that  the  assumed  law  is  true  only  of  a 
.sphere  of  jierfectly  uniform  temperature  at  the  surface,  if  the 
distance  to  the  recipient  of  the  radiating   heat   be   couq)Utcd 


14  RADIANT  HEAT.  CHAP.  I. 

from  the  centre  of  the  hejited  sphere.  Suppose  that  .s,  Fig.  5, 
represents  a  solid  s])here  of  metal  maintained  at  a  constant 
temperature  and  suspended  in  the  centre  of  an  exhausted 
metallic  s])herical  vessel  v,  the  size  of  which  is  much  greater 
tlian  that  of  the  solid  sphere;  c  a  and  c  h  being  radial  lines 
dra\vn  from  the  mutual  centre  c  to  the  circuinference  of  tlie 
exhaiisted  vessel.  The  heated  sphere  being  maintained  at  a 
unifoi'm  temperature  -sA'hile  the  spherical  vessel  is  exhausted, 
and  thereby  freed  from  any  disturbing  influence  of  internal 
currents  of  air,  it  will  be  evident  that  the  intensity  of  radiant 
heat,  thus  transmitted  from  the  sphere  through  the  ether  alone, 
will  be  alike  at  every  point  of  the  surface  of  the  sui-rounding 
sjiherical  vessel.  It  needs  no  demonstration  to  prove  that  the 
temperature  resulting  from  radiation  against  the  latter  will 
be  less  than  that  of  the  central  sphere  in  proportion  to  the 
area  pi'esented  by  each.  In  other  words,  tie  temperature  will 
he  inversely  as  the  areas  of  the  tioo  spheres.  On  the  soundness 
of  this  proposition  depends  the  correctness  of  the  accepted  doc- 
trine I'elating  to  the  propagation  of  heat  and  light  through 
space.  The  remarkable  fact  niTist  not  be  overlooked,  that 
this  projiosition  takes  no  cognizance  of  distance ;  and  that  it 
enables  us  to  determine  the  temperature  of  the  surrounding 
sphere  if  we  know  the  temperature  of  the  central  one,  merely 
l)y  comparing  their  relative  areas,  basing  our  computation  on 
the  proportion  they  bear  to  each  other;  the  intervening  space, 
whether  it  be  1  mile,  or  1,000  miles,  being  an  element  excluded 
from  our  calculation. 

That  rays  of   light  and    heat  meet   with    no    appreciable 


CHAP.  I.  TL'A.\SM1SSI<)X  OF  J:AI)IA.\T  HEAT.  lo 

resistance  in  their  passage  through  the  etlier  is  an  irresistible 
inference  to  be  drawn  from  the  fact  that  the  intensity  bears 
a  direct  pi-oportion  to  the  area  over  which  the  rays  are  di.s- 
]K-rt<ed.  The  conuuoii  expression  that  "tlie  intensity  of  light 
and  heat  varies  inversely  as  the  square  of  the  distances  "  leads 
to  the  supposition  that  distance  is  an  element  to  be  taken  into 
account  in  estimating  the  intensity  of  radiant  heat.  That  this 
is  an  error  will  be  readily  })erceive(l  if  we  reHect  on  the  fact, 
just  referred  to,  that  the  intensity  of  the  rays  diminishes  in 
the  exact  pioportion  to  the  areas  over  which  they  are  dis- 
jiersed.  It  is  self-evident  that  if  distance,  per  se,  in  any  way 
att'ected  the  question,  the  intensities  could  not  thus  depend 
solely  on  the  extent  of  the  areas  over  which  the  rays  are 
diffused.  Much  misapprehension  would  be  prevented  if  the 
law  relating  to  radiant  heat  were  thus  expi-essed :  l^ie  inttii- 
sities  are  inversely  as  the  areas  over  which  the  rays  are  dis- 
persed. Sir  Isaac  Newton,  referring  to  the  intensity  of  the 
sun's  radiant  heat  at  dift'erent  distances,  thus  clearly  defines 
the  question  :  "  The  heat  of  the  sun  (at  various  distances) 
is  as  the  density  of  its  rays."  He  also  states  that  the  den- 
sities of  the  diverging  rays  are  "  reciprocally  as  the  square 
of  the  distance  from  the  centre  of  the  sun,"  a  fact  which 
obviously  has  nothing  to  do  with  the  main  proposition,  as 
it  simply  results  from  certain  geometrical  relations,  viz.,  that 
the  areas  of  transverse  sections  of  a  cone  are  as  the  square 
of  the  distances  from  the  apex. 

I  will  now  briefly  show  why  the  theory  of  Newton,  sup- 
posed to  have  been  proved  by  Melloni,  is  true,  under  certain 


16  BADIANT  HEAT.  chap.  i. 

conditions,  as  regards  a  uniformly  lieated  sphere,  although 
fallacious,  under  all  circumstances,  as  regards  plane  surfaces. 
Referring  again  to  Fig.  5,  let  us  assume  that  the  sphere  ,s 
represents  the  sun,  the  semi-diameter  of  ^vhicll  is  426,2U2 
miles ;  and  that  a  b  v  rejjresents  the  earth's  orbit  reduced  to 
a  circle  whose  radius  corresjiouds  Avith  the  earth's  mean  dis- 
tance from  the  sun's  centre,  viz.,  91,430,000  miles.  Now,  the 
arc  e  f  is  to  the  arc  a  h  as  the  radial  line  <:  e,  rejjresenting  the 
sun's  radius,  is  to  c  a,  re2:)resenting  the  earth's  distance  from 
the  sun's  centre.  According  to  the  stated  dimensions,  there- 
fore, c  e  is  to  c  a  as  1  to  214.44:;  hence,  regarding  a  c  h  as  a 
cone  of  very  small  base,  the  area  of  e  f  is  to  that  of  a  b  as  1  to 
the  square  of  214.44  =  45,984.  Accordingly,  the  temperature 
of  the  heated  central  sphere  «  will  be  45,984  times  greater 
than  the  temi^erature  which  it  imparts  by  radiation  to  the 
sui'rounding  sphere  a  b  v. 

We  have  now  fully  established  the  fact  that,  although  the 
extent  of  the  radiating  and  recipient  surfaces,  in  connection 
with  the  temj^erature  of  the  former,  determines  the  tempera- 
ture transmitted  to  the  latter,  wholly  independent  of  distance, 
yet,  as  regards  the  sun,  it  is  true  that  the  temperature  pro- 
duced by  the  radiant  heat  of  his  rays  is  inversely  as  the 
square  of  the  distance  from  his  centre,  the  same  law  applying 
to  all  spheres  having  a  uniform  temperature  at  the  surface. 


CHAPTER    11. 

EADIATIOX  AT  DIFFERENT  TEMPERATURES. 


SiK  Isaac  Newtox  supposed  that  a  lieated  body  Avould 
lose  by  radiation  at  each  instant  a  quantity  of  heat  propor- 
tionate to  the  excess  of  its  temperature  above  that  of  the  sur- 
rounding medium.  Modern  physicists,  basing  their  reasoning 
on  the  result  of  MM.  Dulong  and  Petit's  experiments,  contend 
that  Newton's  supposition  is  erroneous.  Prof.  Balfour  Ste\vart 
in  his  "  Elementary  Treatise  on  Heat,"  published  at  Oxford 
1871,  in  support  of  his  assertion  that  Newton's  doctrine  is 
false,  presents  the  following  extract  from  the  work  of  Duloug 
and  Petit : 

Excess  of  Temperature  of 

the  Thermometer.  Velocity  of  Cooling. 

°c.  °  c. 

240  10.69 

220  8.81 

200  7.40 


18 


BADIANT  HEAT. 

CHAP.  II. 

Excess  of  Temperature  of 

the  Thermometer.                                     Veloc 

ity  of  Cooling. 

°c. 

°c. 

180 

6.10 

160 

4.89 

140 

3.88 

120 

3.02 

100 

2.30 

' 

80 

1.74 

"We  see  at  once  from  this  table,"  says  the  author  of  the 
"  Elementary  Treatise  on  Heat,"  "  that  the  law  of  Newton 
does  not  hold,  for  according  to  it  the  velocity  of  cooling  for 
an  excess  of  200  deg.  should  be  precisely  double  of  that  for 
an  excess  of  100  deg. ;  now  we  find  that  it  is  more  than  three 
times  as  much."  The  rate  of  cooling  exhibited  in  this  table 
being  at  variance  with  the  laws  which  govern  the  emission 
and  absorption  of  radiant  heat,  I  have  instituted  a  series  of 
experiments  in  order  to  test  the  correctness  of  the  tabulated 
rates  accepted  by  Prof.  Stewart.  The  initiary  proceeding  of 
the  investigation  was  that  of  ascertaining  the  rate  of  cooling 
at  temperatures  beloAV  200°  F.,  for  which  purpose  I  constructed 
the  apparatus  shown  on  PI.  4,  Fig.  1,  representing  three  concen- 
tric spherical  vessels  placed  within  each  other.  As  the  draw- 
ing shows  the  detail  of  the  entire  naechanisra,  a  brief  descrip- 
tion will  suffice,  a  «  is  a  spherical  vessel  7  inches  in  diameter, 
applied  within  an  exterior  casing  h.  A  spherical  radiator  r, 
4  inches  in  diameter,  composed  of  very  thin  copper,  and  coated 
with  lamp-black,  is  sustained  in  the  centre  of  the  spherical 
vessel  a  by  means  of  two  vertical  tubes  I  and  w,  composed 


CHAP.  11.   liAJjJATioy  AT  diffjjuent  tempekatures.  ly 

of  very  thin  metal,  coramuuicatiug  with  the  interior  of  the 
radiator.  The  upper  tube  is  large  enough  to  admit  the  bulb 
of  a  thermometer,  the  lower  one  being  only  sufficiently  large 
to  accommodate  a  small  axle,  to  \vhich  is  attached  a  paddle- 
wheel  provided  with  curved  paddles  arranged  in  such  a  manner 
that  the  bulb  of  the  thermometer  may  be  inserted  consider- 
ably beyond  the  centre  of  the  sphere,  as  shown  in  the  illus- 
ti'ation.  The  external  casing  b  is  provided  with  nozzles  g 
and  d,  to  which  tubes  are  attached  for  circulating  cold  water 
through  the  intervening  space  during  experiments.  The  air  is 
exhausted  from  the  spherical  enclosure  a  a  through  the  tube 
I;  which  passes  across  the  said  intervening  space.  The  radi- 
ating sphere  c  being  filled  with  water,  it  will  be  perceived 
that  the  centrifugal  action  of  the  paddles  of  the  wheel  applied 
within  ^vill  produce  a  continuous  current  from  the  centre  to- 
wards the  circumference,  the  fluid  successively  passing  over 
and  coming  in  contact  with  the  thin  spherical  shell,  then 
returning  to  the  centre  to  be  again  thrown  off  by  the  centri- 
fugal action.  The  rotary  motion  of  the  water  thus  kept  up 
without  inteiTnission  round  the  cylindrical  bulb  of  the  ther- 
mometer, will  evidently  render  its  indication  prompt  and  reli- 
able. It  is  hardly  necessary  to  observe  that  the  rajiid  pre- 
sentation of  fresh  particles  of  A\'ater,  promoted  by  the  action 
of  the  paddles,  will  eflfectually  prevent  the  reduction  of  tem- 
perature proceeding  faster  at  the  circumference  than  at  the 
centre ;  hence  the  radiation  at  the  surface  Avill,  in  virtue  of 
the  continuous  interchange  of  particles,  affect  almost  simul- 
taneously eveiy  molecule  within  the  sphere.     It  will  be  seen, 


^0  RADIANT  HEAT.  CHAP.  ir. 

therefore,  that  the  total  energy  of  radiation  will  be  rendered 
availaljle  in  i-edueing  the  temperature  of  the  contents  of  the 
radiator,  and  tliat  the  central  thermometer  Avill  indicate,  at 
every  instant,  the  precise  degree  of  temperature  of  the  entire 
mass.  It  might  be  sujiposed  that  the  motion  of  the  watei- 
within  the  sphere,  consequent  on  the  action  of  the  paddle- 
wheel,  Avould  produce  an  elevation  of  temperature  sufficient  to 
render  the  indication  of  the  thermometer  inaccurate.  Before 
commencing  the  experiments,  several  trials  were  accordingly 
instituted  to  ascertain  if  at  the  requisite  speed,  20  turns  per 
minute,  heat  could  be  produced.  The  result  has  proved  posi- 
tively that  no  appreciable  elevation  of  temperatui-e  talces  j^lace. 
The  diameter  of  the  wheel  being  3.4  ins.,  the  maximum  speed 
of  the  particles  of  water  produced  by  the  rotation  scarcely 
reaches  3.5  ins.  per  second,  a  velocity  evidently  too  small  to 
generate  appreciable  heat. 

The  mode  of  conducting  the  experiment  Avill  be  seen  by 
the  following  statement :  A  capacious  wooden  cistern,  charged 
with  water  and  crushed  ice,  is  connected  by  small  flexible 
tubes  to  the  nozzles  g  and  d  on  opposite  sides  of  the  external 
vessel  h,  a  pump  being  applied  between  the  said  nozzles  and 
the  cistern,  by  means  of  which  the  cold  water  is  forced  through 
the  apparatus  and  ultimately  returned  to  the  source  of  supply. 

In  view  of  the  great  importance  of  the  question  at  issue 
the  investigation  has  been  conducted  with  the  utmost  care, 
four  operators  having  been  employed  to  cany  out  the  experi- 
ments, th.e  labor  being  thus  divided  :  1st  operator  regulates 
the  temperature  of  the  water  in  the  cistern  by  continual  agita- 


CHAP.  II.     RADIATION  AT  DIFFEREyr  TEMPERATURES.  21 

tiou  and  supply  of  crushed  ice  from  time  to  time  ;  2d  operator 
works  the  pump  at  a  uniform  rate  ;  3d  operator,  after  having 
charged  the  central  .sphere  with  boiling  water,  turns  the  paddle- 
wheel,  reads  the  thermometei",  and  announces  the  temperature 
for  each  degree,  at  the  instant  when  the  toj)  of  the  mercui-ial 
column  is  covered  by  half,  the  thickness  of  the  line  on  the 
scale ;  the  4th  operator,  provided  with  a  Casella  chronograph, 
records  the  time  and  temperature.  It  should  be  ol)sen'ed 
that,  notwithstanding  this  procedure,  there  is  a  slight  ii-re- 
gularity  in  the  ratio  of  temperature  and  time,  the  increment 
for  each  degree  not  being  quite  unifoi-m.  Obviously  the  most 
practised  eye,  though  assisted  by  the  raagnifying-glass,  can- 
not detennine  exactly  at  what  moment  the  top  of  the  falling 
column  is  half  covered  by  the  line  on  the  thermometric  scale. 
Again,  a  pei-fectly  graduated  thermometer  cannot  be  obtained. 
The  discrepancy  referred  to  is,  howevei',  so  small  that  it  can- 
not readily  be  detected  in  the  diagram.  It  will  lie  proper 
to  state  that,  in  constnicting  the  several  tables  contained  in 
this  chapter,  a  correction  has  been  introduced  agreeably  to 
Regnault's  method  of  correcting  the  irregularities  inseparable 
from  thermometric  observations.  Referring  to  the  anne.xed 
tables,  marked  A,  it  will  be  noticed  that  the  rate  at  which 
the  spherical  radiator  cools  has  been  recorded  for  each  degree 
of  differential  temperature  from  150'  to  15\  The  tem])era- 
ture  of  the  surrounding  cold  vessel,  it  will  be  .«een,  is  entered 
in  the  first  column  ;  the  temperature  of  the  radiating  sphere 
in  the  second,  and  its  e.xcess  of  temperatuie  in  the  third 
column.      The  number  of  seconds  occupied    in   rftliiciiig  the 


32 


RADIANT  BEAT. 


A 

Table  showing  the  Eate 

OF  Cooling 

OF    A 

Heated  Body 

SUSPENDED    WITHIN    A    C'of.D   EkCLOSURE. 

Is 

g  o 

a"? 

Is 

EH  !a 
o 

111 
i  1  § 

0-" 

B 
II 

1-1 

11 

o  3 

"3  >;> 
P   . 

"go 

o 

^■^ 

3  ^ 
£  c 

bs,Q 
03  > 

II       ■ 

•JaA. 

°Fah. 

°Fah. 

Sees. 

&(». 

•Fah. 

°Fah. 

°Fah. 

Sece- 

Sees. 

33 

183 

150 

37.7 

42.01 

33 

160 

127 

47.3 

49.64 

H3 

182 

149 

38.1 

42.29 

33 

159 

120 

47.8 

50.04 

33 

181 

148 

38.5 

42.57 

33 

158 

]25 

48.3 

50.44 

33 

180 

147 

38.9 

42.86 

33 

157 

124 

48.8 

50.85 

33 

179 

146 

39.3 

43.16 

33 

156 

123 

49.3 

51.26 

33 

178 

145 

39.7 

43.46 

33 

155 

122 

49.8 

51.68 

33 

177 

144 

40.1 

43.76 

33 

154 

121 

50.3 

52.11 

33 

-  176 

143 

40.5 

44.07 

33 

153 

120 

50.8 

52.55 

33 

175 

142 

40.9 

44.38 

33 

152 

119 

51.3 

53.00 

33 

174 

141 

41.3 

44.69 

33 

151 

118 

51.8 

53.44 

33 

173 

140 

41.7 

45.02 

33 

150 

117 

52.3 

53.90 

33 

172 

139 

42.1 

45.34 

33 

149 

116 

52.8 

54.37 

33 

171 

138 

42.5 

45.67 

33 

148 

115 

53.3 

54.84 

33 

170 

137 

42.9 

46.01 

33 

147 

114 

53.9 

55.33 

33 

169 

136 

43.3 

46.34 

33 

146 

113 

54.5 

55.82 

33 

168 

135 

43.7 

46.69 

33 

145 

112 

55.1 

50.32 

33 

167 

134 

44.1 

47.04 

33 

144 

ni 

55.7 

56.83 

33 

166 

133 

44.5 

47.39 

33 

143 

110 

56.3 

57.35 

33 

165 

132 

44.9 

47.75 

33 

142 

109 

56.9 

57.87 

33 

164 

131 

45.3 

48.12 

33 

141 

108 

57.5 

58.42 

33 

163 

130 

45.8 

48.49 

33 

140 

107 

58.2 

58.97 

33 

102 

129 

46.3 

48.87 

33 

139 

106 

58.9 

59.52 

33 

161 

128 

46.8 

49.25 

;   33 

1 

138 

105 

59.6 

60.09 

Cll.vi'.  II.      liADlATlON  AT  DlFFEliEM  TEMrEliATURES. 


A 

Table  .miowino  thk  Kate 

or  Coo  LI. NO 

OF    A 

Heated   Body 

SUSPENDED    WITHIN   A    COLU    ExCLOSVlit:. 

o 

So 

P 

11 

"3 

O   3 
M  ■" 
'A 

111 

Hi 
Is 

o- 

S 

So    - 

■s 

11 

2.'% 

as 

i1 

S.1 

Observed  time  cool- 
ing enclosed  body 
one  deg. 

2 

ll 
11 

'Fah. 

'Fak 

'Fah. 

Ste». 

Sea. 

•Fah. 

'Fah. 

'Fah. 

Sta. 

Ste». 

33 

137 

104 

60.3 

60.67 

33 

114 

81 

80.8 

78.01 

33 

136 

103 

61.0 

61.27 

33 

113 

80 

81.9 

78.99 

33 

135 

102 

61.7 

61.87 

33 

112 

79 

83.1 

80.00 

33 

134 

101 

62.4 

62.48 

33 

111 

78 

84.3 

81.03 

33 

133 

100 

63.2 

63.11 

33 

110 

77 

85.5 

82.09 

33 

132 

99 

64.0 

63.76 

33 

109 

76 

86.7 

83.18 

33 

131 

98 

64.8 

64.41 

33 

108 

75 

88.0 

84.29 

33 

130 

97 

65.6 

65.08 

33 

107 

74 

89.3 

85.44 

33 

129 

96 

66.4 

65.76 

33 

106 

73 

90.6 

86.62 

33 

128 

95 

67.2 

66.46 

33 

105 

72 

91.9 

87.83 

33 

127 

94 

68.0 

67.16 

33 

104 

71 

93.3 

89.08 

33 

126 

93 

68.9 

67.89 

33 

103 

70 

94.7 

90.36 

33 

125 

92 

69.8 

68.63 

33 

102 

69 

96.1 

91.68 

33 

124 

91 

70.7 

69.39 

33 

101 

68 

97.5 

93.04 

33 

123 

90 

71.6 

70.17 

33 

100 

67 

99.0 

94.44 

33 

122 

89 

72.5 

70.96 

33 

99 

66 

100.5 

95.88 

33 

121 

88 

73.5 

71.77 

33 

98 

65 

102.0 

97.36 

33 

120 

87 

74.5 

72.60 

33 

97 

64 

103.6 

98.89 

33 

119 

86 

75.5 

73.45 

33 

96 

63 

10i).2 

100.48 

33 

118 

85 

76.5 

74.32 

33 

95 

62 

106.9 

102.11 

33 

117 

84 

77.5 

75.21 

33 

94 

61 

108.6 

103.80 

33 

116 

83 

78.6 

76.12 

33 

93 

60 

110.4 

105.55 

33 

115 

82 

79.7 

77.11.) 

33 

92 

59 

112.:! 

107.35 

24 


BADIAM  HEAT. 


A 

Tahle  showing  tue  Rate 

OF  Cooling 

of  a 

Heated  Body 

SUSPENDED    WITHIN    A    COLD   ENCLOSURE. 

"8 

is 
P 

li 

c 

k 

1- 

It 

-S 

ii 

MO 

ail 

H 

O 

a  a> 

£'g 

l1 

CO 

£13 
£  0 
H  I- 

11 

ii 

CO 

o- 

-S 

.be 
^^ 

l| 

'  Fnh. 

'Fall. 

'Fah. 

Sees. 

Sees. 

'Fah. 

'Fah. 

'Fah. 

Secs. 

Sees. 

33 

91 

58 

114.3 

109.22 

33 

69 

36 

189.9 

176.90 

33 

90 

57 

116.4 

111.15 

33 

68 

35 

195.4 

182.03 

33 

89 

56 

118.6 

113.15 

33 

67 

34 

201.2 

187.46 

33 

88 

55 

120.9 

115.23 

33 

66 

33 

207.2 

193.23 

33 

87 

54 

123.3 

117.38 

33 

65 

32 

213.5 

199.36 

33 

86 

53 

125.8 

119.62 

33 

64 

31 

220.2 

205.90 

33 

85 

52 

128.4 

121.94 

33 

63 

30 

227.4 

212.88 

33 

84 

51 

131.1 

124.35 

33 

62 

29 

235.1 

220.35 

33 

S3 

50 

133.9 

126.87 

3:3 

61 

28 

243.4 

228.36 

33 

82 

49 

136.8 

129.48 

33 

60 

27 

252.3 

236.98 

33 

81 

48 

139.9 

132.21 

33 

59 

26 

261.9 

246.27 

33 

80 

47 

143.1 

135.05 

33 

58 

25 

272.2 

256.32 

33 

79 

46 

146.5 

138.02 

33 

57 

24 

283.3 

267.23 

33 

78 

45 

150.0 

141.12 

33 

56 

23 

295.4 

279.11 

33 

77 

44 

153.7 

144.37 

33 

55 

22 

308.7 

292.09 

33 

76 

43 

157.5 

147.76 

33 

54 

21 

323.4 

306.34 

33 

75 

42 

161.5 

151.32 

33 

63 

20 

339.7 

322.05 

33 

74 

41 

165.7 

155.06 

33 

52 

19 

357.9 

339.46 

33 

73 

40 

170.1 

158.99 

33 

51 

18 

378.3 

358.86 

33 

72 

39 

174.7 

163.12 

33 

50 

17 

401.2 

380.60 

33 

71 

38 

179.5 

167.47 

33 

49 

16 

426.9 

405.16 

33 

70 

37 

184.6 

172.06 

33 

48 

15 

455.7 

433.10 

CHAP.  II.     liADlATIOX  AT  l>lFl'EliEM  TEMl'imATVliES.  '^'^ 

temperature  of  the  radiating  spliere  one  degree  is  rec(jrdeil 
iu  the  fourth  column.  The  fifth  column  contains  the  number 
of  second.s  which  A\x)uld  be  requisite  to  reduce  the  tempera- 
ture one  degree  if  the  cooling  proceeded  at  the  rate  shown 
by  the  Newtonian  law. 

Let  ns  now  examine  the  diagram  Fig.  2,  attached  to  the 
illustration,  in  whieli  the  length  of  the  ordinates  of  the  curve 
b  c  represent  the  observed  time  for  each  degree  of  differential 
temperature,  while  the  ordinates  of  the  cun^e  a  d  represent 
the  time  that  would  elapse  if  the  rate  of  cooling  were  in  exact 
accordance  with  Newton's  doctrine — namely,  if  the  times  were 
inversely  as  the  differential  temperatures.  The  vertical  line 
in  Fig.  2,  on  which  the  ordinates  representing  the  time  of 
cooling  liave  been  projected,  is  divided  into  degrees  of  Fah- 
renheit, showing  the  differential  temi^erature,  viz.,  the  excess 
of  temperature  of  the  radiating  sphere  above  that  of  the  sur- 
rounding cold  vessel.  A  careful  inspection  of  this  diagram  and 
of  the  Tables  A,  rendei-s  argument  unnecessarj^  to  show  that 
our  experimental  investigation  has  established  the  correctness 
of  Newton's  assumption  that  a  radiating  body  loses  at  each 
instant  a  quantity  of  heat  proportionate  to  the  excess  of  its 
temperature  above  that  of  the  surrounding  medium.  It  will 
be  sho-wn  hereafter  that  the  slight  discrepancy  indicated  by 
the  different  length  of  the  ordinates  of  the  curves  a  d  and 
i  c  is  owing  to  the  variation  of  emissive  power  of  the  radiator, 
caused  by  the  difference  of  molecular  motion  resulting  fi-om 
change  of  tempeiature,  and  the  consequent  change  of  dimen- 
sions, of  the  radiator.    Dulong  and  Petit's  formula  being  based 


26 


BABIANT  HEAT. 


on  tlie  table  presented  at  the  commencement  of  this  chapter, 
copied  from  Prof.  Stewart's  "Elementary  Treatise  on  Heat" 
(compared  also  with  the  French  original),  I  have  deemed  it 
important  to  examine  carefully  whether  the  rates  of  cooling 
presented  in  the  said  table  arQ  consistent.  The  result  of  this 
examination  is  shown  in  the  accompanying  table,  in  which 
the  1st  column  contains  the  differential  temperature  of  the 
radiator,  the  2d  column  contains  the  corresponding  rate  of 
cooling  for  each  minute,  established  by  Duloug  and  Petit ; 
while  the  3d  and  4th  columns  show  the  ratio  of  difference. 


240° 

10°.  69 

\      1.88 

220 

8.81 

\      1.41 

\      0.47 

200 

7.40 

1   1.30 

j   0.11 

180 

6.10 

(   1.21 

\      0.09 

160 

4.89 

(   1.01 

(   0.20 

140 

3.88 

(   0.86 

I   0.15 

120 

3.02 

(   0.72 

I   0.14 

100 

2.30 

j   0.56 

;   0.16 

80 

1.74 

1 

2 

3 

4 

The  inconsistency  and  irregularity  of  the  rates  of  cooling  exhi- 
bited by  the  figures  in  the  two  last  columns  prove  the  um-e- 
liable  character  of  the  temperatures  inserted  in  the  two  first 
columns.     We  are  warranted  in  concluding  that  a  doctrine 


CHAP.  II.      liADIATIoy  AT  DlFb'EHEST  TKMVKUATUREa. 


2: 


B 


Table  siiowixc;  tiik  Rate  of  Coolint.  of  a  Heatkd  IJody 

SUSPENDED    WITUIN   A    VOLD   EnCI.OSUKK. 


.S-3 


r 


^•5 


3  =8 
ll 


—  B 
B  O   O 


>  g  0 

S  to 

.a  c 
0-" 


i>? 


."2 

E  S 

£1 


c  g 


S'3  Sf 


&e«. 


Cent. 


Ste». 


See*. 


Suit. 


83 

82 

81 

80 

79 

78 

77 

76 

75 

74 

73 

72 

71 

70 

GO 

68 

67 

66 

65 

64 

63 

62 

61 

60 

59 

58 


38.1 

38.8 

39.5 

40.3 

41.0 

41.7 

42.4 

43.1 

43.8 

44.5 

45.3 

46.1 

47.0 

47.9 

48.8 

49.8 

50.7 

51.6 

52.5 

53.5 

54.5 

55.6 

56.7 

57.8 

59.0 

60.3 


42.29 

42.81 

43.34 

43.89 

44.45 

45.02 

45.60 

46.20 

46.82 

47.46 

48.12 

48.80 

49.49 

50.20 

50.93 

51.68 

52.45 

53.25 

54.09 

54.94 

55.82 

56.73 

57.67 

58.64 

59.64 

60.47 


57 

56 

55 

54 

53 

52 

51 

50 

49 

48 

47 

46 

45 

44 

43 

42 

41 

40 

39 

38 

37 

36 

35 

34 

33 

32 


61.6 
62.9 
64.3 
65.7 
67.2 
68.7 
70.3 
72.0 
73.7 
75.5 
77.3 
79.2 
81.2 
83.3 
85.5 
87.7 
90.0 
92.4 
94.9 
97.5 
100.2 
103.0 
106.0 
109.1 
112.3 
115.9 


61.75 
62.86 
64.01 
65.21 
66.46 
67.74 
69.09 
70.48 
71.94 
73.45 
75.02 
76.68 
78.40 
80.20 
82.09 
84.07 
86.14 
88.32 
90.62 
93.04 
95.58 
98.28 
101.12 
104.15 
107.35 
110.76 


31 
30 
29 
28 
27 
26 
25 
24 
23 
22 
21 
20 
19 
18 
17 
16 
15 
14 
13 
12 
11 
10 
9 
8 
7 
6 


119.9 

124.3 

128.9 

133.9 

139.3 

145.2 

151.5 

158.3 

165.7 

173.8 

182.6 

192.1 

202.4 

213.5 

225.7 

239.4 

255.2 

273.6 

295.4 

321.1 

351.6 

388.1 

432.5 

487.9 

558.0 

656.3 


114.39 

118.27 

122.41 

120.87 

131.05 

136.81 

142.40 

148.46 

155.06 

162.27 

170.18 

178.91 

188.59 

190.36 

211.44 

22r).08 

240.01 

258.44 

279.11 

303.38 

332.27 

307.25 

410.45 

405.11 

536.71 

634.33 


28  EADIAKT  HEAT.  CHAP.  ii. 

based  on  sucli  unsatisfactory  premises  cannot  be  sound.  How 
far  this  inference  is  correct  will  be  seen  presently,  by  a  com- 
parison between  tlie  ratio  of  cooling  at  liigli  temperatures, 
deduced  from  MM.  Duloug  and  Petit's  formula,  and  the  actual 
rate  shown  by  an  incandescent  cast-iron  sphere  enclosed  within 
a  vacuum ;  also  by  the  amount  of  mechanical  energy  developed 
by  the  radiation  of  fused  cast  iron.  The  temperatures  inserted 
in  the  table  mai'ked  B,  relating  to  the  experiments  under  con- 
sideration, have  been  reduced  to  the  Centigrade  scale  for  the 
purpose  of  facilitating  direct  comparison  with  the  result  of 
Dulong  and  Petit's  researches. 

The  question  has  frequently  been  asked,  whether  Newton's 
law  holds  for  mcrease  of  temperature  when  a  cold  body  is 
exposed  to  the  radiation  of  a  surrounding  hot  medium.  In 
order  to  decide  the  question,  experimentally,  whether  the  times 
occupied  in  heating  a  certain  body  are  equal,  for  corresponding 
differential  temperatures,  to  the  times  occupied  in  cooling  the 
same  body,  a  modified  apparatus  has  been  constructed  (see 
illustration  shown  on  Plate  5,  Fig.  3).  The  means  adopted 
for  measuring  the  temperature  and  producing  circulation  Avithin 
the  central  sphere  being  identical  with  those  of  the  apparatus 
already  described,  it  will  only  be  necessary  to  point  out  that 
the  exhausted  vessel  a  a  which  suiTounds  the  central  sphere 
c  is  immersed  in  water  contained  in  a  cylindrical  vertical 
boiler  b,  open  at  the  top  and  heated  by  means  of  a  spirit- 
lamp  applied  under  its  bottom.  The  experiments  with  this 
modified  apparatus  have  been  conducted  in  the  following 
manner:    The   water  in  the  boiler  havina:  been   brought  to 


CHAP.  II.       UADIATION  AT  DIFFEUEST  TEMl'EliATUREa. 


29 


c 

Table  showing 

THE  Eate  of  Heating  of 

A  Cold  Body 

SUSPENDED  WITHIN 

A  Heated 

Enclosure. 

'o 
So 

53 
1  = 

is 

ss 

M  3 

•°  9, 

IS 

Time  agreeably  to 
Newton's  law. 

gi 
H 

s-g 

B 

o 

u 

~  a 
o  ^ 
H.  ° 

X  3 

o 

II 

'  FaK. 

'Fah. 

'FaK 

Sect. 

Stct. 

'Fah. 

'Fah. 

'Fah. 

Sea. 

StM. 

212 

37 

175 

29.1 

29.08 

212 

64 

148 

35.6 

34.41 

212 

38 

174 

29.3 

29.25 

212 

65 

147 

35.9 

34.64 

212 

39 

173 

29.5 

29.42 

212 

66 

146 

36.3 

34.88 

212 

40 

172 

29.7 

29.59 

212 

67 

145 

36.5 

35.12 

212 

41 

171 

29.9 

29.76 

212 

68 

144 

36.8 

35.36 

212 

42 

170 

30.1 

29.94 

212 

69 

143 

37.1 

35.01 

212 

43 

169 

30.3 

30.12 

212 

70 

142 

37.4 

35.86 

212 

44 

168 

30.5 

30.29 

212 

71 

141 

37.7 

36.12 

212 

45 

167 

30.7 

30.48 

212 

72 

140 

38.0 

36.38 

212 

46 

166 

30.9 

30.66 

212 

73 

139 

38.3 

36.64 

212 

47 

165 

31.1 

30.85 

212 

74 

138 

38.6 

36.91 

212 

48 

164 

31.3 

31.04 

212 

75 

137 

38.9 

37.18 

212 

49 

163 

31.5 

31.23 

212 

76 

136 

39.2 

37.46 

212 

50 

162 

31.7 

31.42 

212 

77 

135 

39.5 

37.74 

212 

51 

161 

31.9 

31.62 

212 

78 

134 

39.8 

38.02 

212 

52 

160 

32.1 

31.82 

212 

79 

133 

40.1 

38.30 

212 

53 

159 

32.3 

32.02 

212 

80 

132 

40.4 

38.59 

212 

54 

158 

32.6 

32.22 

212 

81 

131 

40.7 

38.88 

212 

55 

157 

32.9 

32.43 

212 

82 

130 

41.0 

39.18 

212 

56 

156 

33.2 

32.64 

212 

S3 

129 

41.3 

39.49 

212 

57 

155 

33.5 

32.85 

212 

84 

128 

41.6 

39.80 

212 

58 

154 

33.8 

33.06 

212 

85 

127 

41.9 

40.12 

212 

59 

153 

34.1 

33.28 

212 

86 

126 

42.2 

40.44 

212 

60 

152 

34.4 

33.50 

212 

87 

125 

42.5 

40.76 

212 

61 

151 

34.7 

33.72 

212 

88 

124 

42.8 

41.09 

212 

62 

150 

35.0 

33.95 

212 

89 

123 

43.1 

41.43 

212 

63 

149 

35.3 

34.18 

212 

90 

122 

43.5 

41.77 

30 


BADIAXT  UEAT. 


c 

Tablk  snowixG 

THE    IiATE    OF   HeaTIXG    OF 

A  Cold 

Body 

SUSPKXDED    WITIIIX 

A  Heated 

ENCLOSURE. 

o 

-S  3 

as 
P 

If 

f=  o 
II 

•s,  ° 

is  of 

-a"  g 
>  g  5 

i  ti 

J  a 

0-" 

o 

|| 

1  ^ 

o 

si 

II 
si 

So 

II 

it 

>  S  o 
•°.5 

'  Fah. 

'Fah. 

'I-ah. 

5eos. 

Sees. 

'Fali. 

°  Fah. 

'Fah. 

Sec». 

S(C3. 

212 

91 

121 

43.9 

42.12 

212 

118 

94 

55.4 

54.28 

212 

92 

120 

44.3 

42.47 

212 

119 

93 

55.9 

54.86 

212 

93 

119 

44.7 

42.83 

212 

120 

92 

56.4 

55.46 

212 

94 

118 

45.1 

43.19 

212 

121 

91 

56.9 

56.08 

212 

95 

117 

45.5 

43.56 

212 

122 

90 

57.4 

56.70 

212 

96 

116 

45.9 

43.94 

212 

123 

89 

57.9 

57.33 

212 

97 

115 

46.3 

44.32 

212 

124 

88 

58.5 

68.00 

212 

98 

114 

46.7 

44.71 

212 

125 

87 

59.1 

58.68 

212 

99 

113 

47.1 

45.11 

212 

126 

86 

59.7 

59.36 

212 

100 

112 

47.5 

45.51 

212 

127 

85 

60.3 

60.06 

212 

101 

111 

47.9 

45.93 

212 

128 

84 

60.9 

60.78 

212 

102 

110 

48.3 

46.35 

212 

129 

83 

61.5 

61.51 

212 

103 

109 

48.7 

46.78 

212 

130 

82 

62.1 

62.27 

212 

104 

108 

49.1 

47.21 

212 

131 

81 

62.7 

63.04 

212 

105 

107 

49.5 

47.65 

212 

132 

80 

63.4 

63.84 

212 

106 

106 

49.9 

48.10 

212 

133 

79 

64.1 

64.65 

212 

107 

105 

50.3 

48.56 

212 

134 

78 

64.8 

65.48 

212 

108 

104 

50.7 

49.03 

212 

135 

77 

65.5 

66.34 

212 

109 

103 

51.1 

49.51 

212 

136 

76 

66.2 

67.22 

212 

110 

102 

51.5 

50.00 

212 

137 

75 

66.9 

68.12 

212 

111 

101 

51.9 

50.50 

212 

138 

74 

67.7 

69.05 

212 

112 

100 

52.4 

51.01 

212 

139 

73 

68.5 

70.00 

212 

113 

99 

52.9 

51.52 

212 

140 

72 

69.3 

70.98 

212 

114 

98 

53.4 

52.05 

212 

141 

71 

70.1 

71.98 

212 

115 

97 

53.9 

52.59 

212 

142 

70 

70.9 

73.02 

212 

116 

96 

54.4 

53.14 

212 

143 

69 

71.8 

74.09 

212 

117 

95 

54.9 

53.70 

212 

144 

08 

72.7 

75.19 

CHAP.  II.      RADIATION  AT  DIFFEREXT  TEMPEBATCRES. 


31 


c 

Table  showinm; 

Tin:  1!at 

:  01'  IfKATLVG  OF 

V  Cold 

Bom- 

SLSPENDEU  WnillX 

A  Ilk 

Vl  TKIJ 

EMLOHLh-t:. 

II 

ll 

CO 

Co 

|S 

.£.■3 

^  c 
S  0 

t  s 

■=1 

lii 
0- 

Time  ng^reeably  to 
Newton's  law. 

0 

11 

=  1 

0 

is 

0^ 

i  p 

Observed  time  lie«t- 

ing  eiiclo.'«<l  body 

one  dcg. 

0 

1 

r 

'r<lh. 

'FaA. 

'Fa?>. 

Sto. 

Sax. 

•Fa/i. 

'Fa/i. 

'fah. 

Stet. 

Stei. 

212 

145 

67 

73.6 

70.32 

212 

172 

40 

118.7 

128.48 

212 

146 

06 

74.5 

77.48 

212 

173 

39 

121.6 

131.82 

212 

147 

65 

75.5 

78.68 

212 

174 

38 

124.6 

135.33 

212 

148 

64 

76.5 

79.92 

212 

175 

37 

127.8 

139.04 

212 

149 

63 

77.5 

81.20 

212 

176 

36 

131.2 

142.96 

212 

150 

62 

78.6 

82.52 

212 

177 

3."") 

134.8 

147.10 

212 

151 

61 

79.7 

83.88 

212 

178 

34 

VSS.G 

151.49 

212 

152 

60 

80.8 

85.29 

212 

179 

33 

142.6 

150.15 

212 

153 

59 

82.0 

86.75 

212 

180 

32 

146.9 

161.11 

212 

154 

58 

83.2 

88.26 

212 

181 

31 

151.5 

166.39 

212 

155 

57 

84.5 

89.82 

212 

182 

30 

156.4 

172.03 

212 

156 

56 

85.8 

91.44 

212 

183 

29 

161.6 

178.07 

212 

157 

55 

87.2 

93.12 

212 

184 

28 

167.1 

184.54 

212 

158 

54 

88.6 

94.86 

212 

185 

27 

172.9 

191.51 

212 

159 

53 

90.1 

96.66 

212 

186 

26 

179.1 

199.01 

212 

160 

52 

91.7 

98.54 

212 

187 

25 

185.7 

207.14 

212 

161 

61 

93.4 

100.50 

212 

188 

24 

192.7 

215.95 

212 

162 

50 

95.2 

102.53 

212 

189 

23 

200.3 

225.55 

212 

163 

49 

97.1 

104.64 

212 

190 

22 

208.7 

236.05 

212 

164 

48 

99.1 

106.84 

212 

191 

21 

218.1 

247.56 

212 

165 

47 

101.2 

109.14 

212 

192 

20 

228.7 

260.26 

212 

166 

46 

103.4 

111.54 

212 

193 

19 

240.7 

274.32 

212 

167 

45 

105.7 

114.05 

212 

194 

18 

254.7 

289.99 

212 

168 

44 

108.1 

116.66 

212 

195 

17 

269.6 

307.57 

212 

169 

43 

110.6 

119.41 

212 

196 

16 

287.0 

327.42 

212 

170 

42 

113.2 

122.29 

212 

197 

15 

306.8 

350.00 

212 

171 

41 

115.9 

125.31 

32 


RADIANT  HEAT. 


c 

Table  siiowtxo  the  Kate 

OF  Heating  of 

A  Cold  Body 

SUSPENJMiD 

WITHIN  A  Hot 

Enci.osuhe. 

-3 

11 

"a 

too 

Differential  tem- 

pei'atui-e  of  enclosed 

body. 

J|l 
11  i 

II 

H 

Differential  tem- 
perature of  enclosed 
body. 

Obsen'ed  time  heat- 
ing enclosed  body 
one  deg. 

E-i 

'Cent. 

Sees. 

Sec«. 

'Cent. 

Sees. 

Sees. 

°  Cent. 

Sees. 

Sees. 

97 

29.3 

29.22 

67 

44.2 

42.40 

37 

74.4 

11. ^A: 

96 

29.6 

29.52 

66 

44.9 

43.04 

36 

76.1 

79.42 

95 

30.0 

29.83 

65 

45.6 

43.71 

35 

78.0 

81.72 

94 

30.3 

30.15 

64 

46.4 

44.40 

34 

79.9 

84.16 

93 

30.7 

30.48 

63 

47.1 

45.11 

33 

82.0 

86.75 

92 

31.1 

30.81 

62 

'47.8 

45.84 

32 

84.2 

89.50 

91 

31.4 

31.15 

61 

48.5 

46.60 

31 

86.6 

92.44 

90 

31.8 

31.50 

60 

49.3 

47.38 

30 

89.2 

95.57 

89 

32.2 

31.86 

59 

60.0 

48.19 

29 

92.0 

98.92 

88 

32.6 

32.22 

68 

50.7 

49.03 

28 

95.2 

102.53 

87 

33.1 

32.60 

57 

51.4 

49.90 

27 

98.7 

106.39 

86 

33.6 

32.99 

66 

52.2 

60.80 

26 

102.5 

110.56 

85 

34.2 

33.38 

55 

53.1 

51.73 

25 

106.6 

115.04 

84 

34.8 

33.78 

54 

54.0 

52.69 

24 

111.1 

119.97 

83 

35.3 

34.18 

53 

54.9 

53.70 

23 

115.9 

125.31 

82 

35.8 

34.59 

52 

55.7 

54.74 

22 

121.0 

131.13 

81 

36.4 

35.02 

51 

56.6 

55.83 

21 

126.6 

137.63 

80 

36.9 

35.46 

50 

57.6 

56.96 

20 

132.7 

144.58 

79 

37.4 

35.91 

49 

58.6 

58.13 

19 

139.4 

152.40 

78 

38.0 

36.38 

48 

59.7 

69.36 

18 

146.9 

161.11 

77 

38.5 

36.86 

47 

60.8 

60.63 

17 

156.4 

170.87 

76 

39.0 

37.34 

46 

61.9 

61.96 

16 

164.9 

181.89 

75 

39.6 

87.84 

45 

63.0 

63.35 

15 

175.4 

194.44 

74 

40.1 

38.35 

44 

64.2 

64.81 

14 

187.1 

208.84 

73 

40.7 

38.88 

43 

65.5 

66.34 

13 

200.3 

225.56 

72 

41.2 

39.42 

42 

66.8 

67.91 

12 

216.3 

245.16 

71 

41.8 

39.98 

41 

68.2 

69.61 

11 

235.9 

268.52 

70 

42.3 

40.56 

40 

69.6 

71.37 

10 

260.7 

296.77 

69 

42.9 

41.16 

39 

71.1 

73.23 

9 

291.0 

331.69 

68 

43.5 

41.77 

38 

72.7 

75.19 

8 

327.3 

375.90 

CHAP.  II.     liADlAllOS  AT  iniFKUEyr  TEMVEUATLRES.  -i'd 

the  boiling  point,  cold  water,  as  near  the  freezing  point  as 
possible,  is  pumped  into  the  central  sphere,  through  suitable 
2)ipes  (the  thermometer  having  been  previously  removed). 
The  operation  of  charging  with  cold  water  should  be  per- 
formed quickly,  and  the  thermometer  inserted  as  soon  as  the 
sphere  is  full.  The  reading  should  then  commence  without 
a  moment's  delay,  the  temperature  being  announced  for  each 
degree,  and,  together  with  the  time,  recorded  by  the  operator 
attending  the  chronograph,  precisely  as  before  stated  with 
reference  to  the  process  of  ascertaining  the  time  of  cooling. 
The  result  of  tin-  oxperinieut  with  the  ai)iiaratus  under  con- 
sideration will  be  found  by  inspecting  the  annexed  tables  C 
together  with  the  diagram  attached  to  the  illustration,  see 
Fig.  4,  in  which  the  ordinates  of  the  curve  a  h'  b  represent 
the  observed  time  for  each  degree  of  differential  tempera- 
ture, while  the  ordinates  of  the  curve  a  c'  c  represent  the 
time  that  would  elapse  if  the  rate  of  heating  were  in  exact 
accordance  with  Newton's  doctrine.  The  small  amount  of 
the  discrepancy  shown  by  the  diagram  and  table,  at  differ- 
ential temperatures  exceeding  75°  F.,  proves  that  the  energy 
varies  in  accordance  with  dynamical  laws,  whether  heat  be 
parted  with  by  radiation  towards  a  cooler  body,  or  whether 
heat  be  received  from  a  radiating  surrounding  medium  of 
higher  temperature.  The  perceptible  discrepancy  at  low  dif- 
ferential temperature  exhibited  in  the  diagram,  namely,  the 
observed  times  being  shorter  than  the  theoretical  times,  is 
owing  to  the  unavoidable  conduction  of  heat  from  the  boiler 
to   the    cold    central   sphere    through    the    connecting   tubes 


34  BADIANT  HEAT.  chap.  ii. 

/  and  VI.  Obviously  the  prolonged  period  of  heating  conse- 
quent on  low  differential  temperature  renders  the  effect  of  con- 
duction appreciable,  as  indicated  by  the  diagram.  Our  experi- 
ments, then,  establish  the  fact  that  until  the  emissive  power 
is  changed  by  disturbing  causes,  the  energy  developed  by 
radiation  increases  in  the  exact  ratio  of  the  differential  tem- 
peratures. 

It  is  proper  to  mention  that  one  of  the  principal  objects  of 
my  investigations  relating  to  the  velocity  of  cooling  by  radia- 
tion, has  been  that  of  disproving  the  correctness  of  the  assumj)- 
tion  Avhich  certain  eminent  physicists  have  based  on  Dulong 
and  Petit's  estimates  of  the  increase  of  radiant  enei-gy  deve- 
loj^ed  at  high  temperatures.  Radiation,  in  a  dynamic  point 
of  view,  being  merely  transmission  of  mechanical  j^ower,  it 
will  be  evident,  on  reflection,  that  we  need  only  ascertain  the 
number  of  thermal  units  developed  in  a  given  time,  by  a 
given  amount  of  radiating  surface  maintained  at  a  certain  tem- 
perature, in  order  to  determine  the  intensity  which  Dulong 
and  Petit  endeavored  to  deduce  from  the  velocity  of  cooling 
shown  by  the  contraction  of  mercury  and  other  fluids.  It 
must  be  inferred,  from  their  having  adopted  a  method  so  un- 
satisfa,ctory,  that  these  physicists  overlooked  the  fact  that 
radiant  intensity  is  most  accurately  measured  by  ascertaining 
the  amount  of  thermal  energy  developed  in  a  given  time  ; 
and  that  they  deemed  it  impossible  to  determine,  l)y  direct 
means,  tlie  velocity  of  cooling  of  incandescent  bodies.  It  can- 
not be  supposed  that  such  skilful  experimentalists  as  Diilong 
and  Petit  questioned  the  practicability  of  suspending  an  in- 


UHAi'.  II.     EAniATlOX  AT  1HI-FEI:EM  TEMrEh'ATCRES.  X> 

candescent  body  within  a  vaciiuni  surrounded  by  a  coolin'^ 
medium.  Why,  then,  it  may  be  asked,  did  they  not  resort 
to  that  obvious  method  whicli,  if  adopte'd,  would  at  once 
have  convinced  them  of  tlie  fallacy  of  tlioir  formula  assifrn- 
ing  a  fabulous  rate  of  velocity  of  cooling  to  incandescent 
bodies  ?  We  must  infer  that  they  did  not  deem  it  practi- 
cable to  construct  an  instrument  by  which  the  temperature 
of  the  enclosed  incandesctMit  body  could  be  accui'atclv  mea- 
sured. It  will  be  urged  in  defence  of  Dulong  and  Petit's 
method,  that  the  time  occupied  in  cooling  cannot  be  ascer- 
tained e.xactly  unless  an  instrument  can  be  devised  capable 
of  showing  the  temperature  of  incandescent  liodies.  This 
objection,  apparently  valid  since  we  possess  no  reliable  and 
delicate  pyrometer,  falls  to  the  ground  before  the  fact  that, 
at  a  constant  distance,  the  temperatures  impai-ted  to  a  ther- 
mometer by  radiation  are  proportionate  to  the  temperatures 
of  the  radiator ;  and  that  consequently  the  velocity  of  cooling 
of  a  radiator  at  any  temperature  whatever  may  be  ascertained 
by  a  distant  thermometer  as  con-ectly  as  by  one  in  actual  con- 
tact. Before  entering  on  a  description  of  the  method,  before 
referred  to,  of  measuring  the  radiant  energy  at  high  tempei-a- 
tures  by  ascertaining  the  amount  of  thermal  energy  developed 
in  a  given  time  by  a  given  area,  I  will  now  l)riefly  describe 
an  instrument  constructed  in  accordance  with  the  fact  just 
mentioned,  that  the  teinperatures  of  a  recipient  of  radiant  heat 
are  proportionate  to  the  temperatures  of  the  radiator.  The 
illustration  on  Plate  G,  Fig.  5,  represents  a  veitical  section 
and   top    view    of    the    instrument    referred    to,  by  means  of 


36  EAIUANT  HEAT.  CHAP.  II. 

^vliich  the  velocity  of  cooling  of  an  incandescent  l)ody  may- 
be ascertained  M-ith  perfect  accuracy.  Description :  a  a,  sphe- 
rical vessel  composed  of  thin  copper,  coated  with  lamp-black 
on  the  inside  and  provided  with  a  cover  h  fitting  air-tight 
against  the  top  side  of  a  ring  secured  to  the  upper  part  of 
the  spherical  vessel,  the  cover  and  the  ring  being  ground  to- 
gether in  order  to  dispense  with  packing,  c  c,  an  open  cylin- 
drical vessel  through  which  a  constant  stream  of  cold  water 
is  circulated  by  means  of  a  force-pump  and  flexible  tubes 
attached  at  d  and  e,  these  tubes  communicating  with  a  cis- 
tern in  which  water  is  maintained  at  a  constant  temperature 
of  33°  F.  A"  is  a  solid  sphere  of  cast  iron  suspended  by  means 
of  a  lug  formed  at  the  upper  part  of  the  sphere,  secured  under 
the  cover  b  as  shown  by  the  drawing.  A  brass  stopple  ff, 
fitting  air-tight  in  a  conical  socket  formed  in  the  before-men- 
tioned ring,  supports  a  Casella  thermometer  /.  The  cover  b 
is  provided  with  a  vertical  handle  b'  in  order  to  facilitate  the 
operation  of  inserting  the  solid  sphere  A',  after  being  heated 
and  suspended  under  the  cover.  The  air  is  exhausted  from 
the  spherical  vessel  by  means  of  a  large  air-pump,  a  stop- 
cock being  inserted  in  the  exhaust  pipe  at  /.  The  mode  of 
operation  will  be  readily  understood  by  the  following  expla- 
nation. The  solid  cast-iron  sphere  being  brought  to  nearly 
white  heat  in  an  air-furnace,  is  removed  by  suitable  tongs 
and  suspended  under  the  cover  b,  which  latter  is  quickly  put 
in  position  over  the  opening  of  the  spherical  vessel.  The 
air-pump  is  put  in  rapid  motion  immediately  after  putting 
on  the  cover ;  a  few  strokes  of  the  water-pump  being  required 


CHAP.  II.      EADIATWS  AT  DIFFERENT  TEMVEFxATUREa.  37 

to  fill   the  cistern  r  c  to  the  height  shown  in   the  drawing. 
These  operations  being  performed  with  due  diligence,  practice 
has  shown  that  the  temperature  of  the  incandescent  sphere 
will  not  fall  below  1,GUU"  F.  before  the  vacuum  is  sufficiently 
complete  to  admit  of  recording  the  indicated   temperatures. 
The  thermometer  /  being  secured  firmly  in  the  stopple  <j,  may 
of  course  be  inserted  very  quickly,  an  important  circumstance, 
since  the  bulb,  in  order  to  save  time,  should  be  previously 
heated  to  nearly  maxinmm  temperature.     We  have   already 
pointed   out  that,  agreeably  to  the  laws  which   govern   the 
transmission  of  radiant  heat,  the  temperatures  produced  by 
radiation  at  constant  distances  are  proportionate  to  the  tem- 
peratures of  the  radiating  body.     It  will  be  readily  perceived, 
therefore,  that  the  thermometer  /  will  correctly  indicate  the 
raie  of  cooling  of  the  suspended  incandescent  sphere.     But 
in  order  to  prove  the  fallacy  of  Dulong  and  Petit's  estimate 
of  the  rate  of  cooling  at   high  temperatures,  we  must   also 
ascertain  the  temperature  of  the  sphere  itself.      Bearing  in 
mind  that   the   temperature   of  the  recipient  of  radiant  heat 
is  proportionate  to  that  of  the  radiator,  it  ^vill  be  perceived, 
on  reflection,  that  we  can  previously  determine  the  ratio  be- 
tween the  temperature  of  the  sphere  A' and  that  of  the  record- 
ing themometer  /.     Evidently  this  latio  may  be  ascertained 
at  temperatures  which  admit  of  the  emplo^Tuent  of  ordinary' 
mercurial  thermometers,  hence  the  determination  may  be  very 
exact.     It  will  be  readily  understood  that  the  thermometer 
intended  for  our  investigati.m  may  be  placed  at  such  a  dis- 
tance from  a  radiating   spheiical   vessel  containing   mercuiy 


38  EADIAXT  HEAT.  cuap.  it. 

maiiitaiued  at  a  temperature  of  400",  tliat  its  indication  shall 
be  exactly  100°.  In  other  words,  the  distance  between  the 
radiator  and  the  recording  theiTQometer  may  be  such  that  the 
temperature  of  the  former  shall  be  exactly  four  times  greater 
than  the  temperature  of  the  latter.  Now,  if  we  remove  the 
spherical  vessel  referred  to  and  substitute  an  incandescent 
sphere  whose  diameter  corresponds  with  the  outside  diameter 
of  the  said  vessel,  the  indication  of  the  recording  thermometer 
multiplied  by  4  will  show  the  temperatiire  of  the  incandes- 
cent sphere.  It  is  hardly  necessary  to  point  out,  that  much 
time  would  be  wasted  in  the  tedious  process  of  determining 
experimentally  the  distance  between  the  recording  thermo- 
meter and  the  radiator,  necessary  to  cause  an  indication  of 
the  former  exactly  one-fourth  of  the  temperature  of  the  latter. 
Obviously  a  less  symmetrical  coefficient  will  answer  nearly 
as  well  as  the  one  mentioned.  Let  us  therefore  ascertain, 
approximately,  how  near  the  recording  thermometer  may  be 
placed  fi'om  an  incandescent  sphere  of  the  intended  size,  in 
order  that  the  mercuiy  in  the  bulb  may  not  be  brought  to 
boiling  heat.  Having  determined  the  distance  of  the  thermo- 
meter as  stated,  we  may,  without  further  experimenting,  con- 
struct our  instrument  as  shown  by  the  illustration.  The  sphe- 
rical vessel  containing  mercury  being  then  introduced  and  a 
vacuum  fomied  within  the  surrounding  enclosure,  the  tempe- 
rature of  the  said  spherical  vessel,  compared  with  the  tempe- 
rature indicated  by  the  recording  thermometer,  will  of  course 
determine  the  coefficient  of  the  instrument.  The  following 
brief  explanation  of  the  procedure  will  suffice.     Suppose  that 


CH.U'.  n.      RADIATION  AT  DIFFERENT  TEMPEIiArURES.  :iO 

the  temperature  of  the  mercury  in  the  spherical  vessel  is  409° 
while  that  indicated  by  the  recording  thermometer  is  UM". 
The  ratio  of  temperature  between  the  radiator  and  the  record- 
ing thermometer  will  then  be  as  409  to  98  ;  and  hence  the 

.„  ,      409 
coemcient  sought  will  he  —  =  4.173.     Consequently,  if  we 

suspend  the  incandescent  sphere  K  within  the  enclosure  as 
before  directed,  and  tind  by  observation  that  the  recordin*' 
thermometer  indicates  401°,  we  then  learn  that  the  tempera- 
ture of  the  enclosed  incandescent  body,  at  the  moment  of 
observation,  is  4.173  X  401  =  1,673°  F.  The  means  thus 
afforded  of  measuring,  with  great  exactness,  the  temperature 
and  radiant  intensity  of  incandescent  bodies,  cannot  fail  to 
facilitate  future  thermic  investigations. 

The  result  of  our  experiments  with  the  suspended  incan- 
descent sphere,  \n\\  be  found  recorded  in  the  annexed  set  t)f 
tables,  the  first  series,  marked  D,  being  constructed  to  the 
Fahrenheit  scale,  while  the  second  series  E  has  been  reduced 
to  the  Centigrade  scale.  The  fii-st  column  in  Table  D  shows 
the  temperature  of  the  enclosiire,  the  tenipei-ature  of  the  radi- 
ating sphere  being  inserted  in  the  second  column.  The  excess 
of  tem2:)erature  of  the  radiator  over  that  of  the  surrounding 
cold  vessel  will  l)e  fVnuid  in  the  thu'd  column,  the  time  actu- 
ally occupied  in  reducing  the  temperatuie  of  the  radiator  10" 
F.  being  entered  in  the  fourth  column.  The  time  of  cooling, 
agreeably  to  the  Newtonian  law,  will  l)e  found  in  the  fifth 
and  last  column.  The  mode  of  constructing  the  ta1)lrs  will 
be  readily   comprehended    by  referring   to    previous    explaiia- 


40 


BADIAXT  HEAT. 


D 

Table  showing  the  Kate 

OF  Cooling  of  an 

1 
Incandescent 

Solid  Spheue  suspended  within  a  Cold  Enclosuue.         | 

1 

c'_o 

-S 
1^ 

B  9 

el 

h 

c  o 

h 

o 

£"(3 
tJO  o 

Bll 
e5 

i^   o 
|| 
H 

II 

^g 

1^  "  S 

o 

Eh 

'FM. 

°Fnh. 

°  Ji-'iA. 

Seea. 

Seas. 

•  Fah. 

'Fuh. 

'  Fah. 

Seed. 

Sees. 

34 

1600 

1566 

22.24 

21.97 

34 

1320 

1286 

30.77 

26.65 

34 

1590 

1556 

22.48 

22.11 

34 

1310 

1276 

31.17 

26.85 

34 

1580 

1546 

22.72 

22.25 

34 

1300 

1266 

31.58 

27.06 

34 

1570 

1536 

22.96 

22.39 

34 

1290 

1256 

32.00 

27.27 

34 

1560 

1526 

23.21 

22.54 

34 

1280 

1246 

32.42 

27.48 

34 

1550 

1616 

23.46 

22.68 

34 

1270 

1236 

32.85 

27.70 

34 

1540 

1506 

23.72 

22.83 

34 

1260 

1226 

33.28 

27.92 

34 

1530 

1496 

23.98 

22.98 

34 

1250 

1216 

33.72 

28.15 

34 

1520 

1486 

24.25 

23.13 

34 

1240 

1206 

34.16 

28.38 

34 

1510 

1476 

24.52 

23.28 

34 

1230 

1196 

34.61 

28.61 

34 

1500 

1466 

24.80 

23.44 

34 

1220 

1186 

35.06 

28.84 

34 

1490 

1456 

25.08 

23.60 

34 

1210 

1176 

35.52 

29.08 

34 

1480 

1446 

25.37 

23.76 

34 

1200 

1166 

35.99 

29.32 

34 

1470 

1436 

25.66 

23.92 

34 

1190 

1156 

36.47 

29.57 

34 

1460 

1426 

25.96 

24.08 

34 

1180 

1146 

36.95 

29.82 

34 

1450 

1416 

26.26 

24.25 

34 

1170 

1136 

37.44 

30.08 

34 

1440 

1406 

26.57 

24.42 

34 

1160 

1126 

37.94 

30.34 

34 

1430 

1396 

26.88 

24.59 

34 

1150 

1116 

38.44 

30.61  - 

34 

1420 

1386 

27.20 

24.77 

34 

1140 

1106 

38.95 

30.88 

34 

1410 

1376 

27.52 

24.95 

34 

1130 

1096 

39.47 

31.15 

34 

1400 

1366 

27.85 

25.13  ' 

34 

1120 

1086 

40.00 

31.43 

34 

1390 

1356 

28.18 

25.30 

34 

1110 

1076 

40.54 

31.71 

34 

1380 

1346 

28.52 

25.48 

34 

1100 

1066 

41.08 

32.00 

34 

1370 

1336 

28.87 

25.67  1 

34 

1090 

1056 

41.63 

32.30 

34 

1360 

1326 

29.23 

25.86  1 

34 

1080 

1046 

42.19 

32.60 

34 

1350 

1316 

29.60 

26.05 

34 

1070 

1036 

42.76 

32.91 

34 

1340 

1306 

29.98 

26.25 

34 

1060 

1026 

43.34 

33.22 

34 

1330 

1296 

30.37 

26.45 

34 

1050 

1016 

43.93 

33.54 

CHAP.  II.      EAIHJ  lloX  AT  DIFFEliEXT  TEMl'KUMrREa. 


41 


D 

T.\BLF,  SIIOWINO  THF 

Rate  of  Cooling 

OF  AN 

[NCAN  DESCENT 

Solid  Sphere  suspended  within  a 

Cold  Enclosuke.        j 

o 
E  u 

Hi 
"3 

1" 

it 

o 

2. 

H 

u 

H 

£•1 

b*  i 

S.1 

so  . 
■2  =  1 

Observed  time  cool- 
ing enclosed 
sphere  ten  degs. 

2 

1 

1 
1^ 

'Fah. 

'Fah. 

•Fiih. 

S»a. 

8ta. 

'Fah. 

-Fah. 

'Fah. 

Stet. 

Stct. 

34 

1040 

lOOG 

44.53 

33.80 

34 

760 

726 

72.05 

46.42 

34 

1030 

996 

45.15 

34.19 

34 

750 

716 

73.60 

47.04 

34 

1020 

986 

45.79 

34.53 

34 

740 

706 

75.33 

47.68 

34 

1010 

976 

46.45 

38.87 

34 

730 

696 

77.06 

48.34 

34 

1000 

966 

47.12 

35.22 

34 

720 

686 

78.85 

49.01 

34 

990 

956 

47.81 

35.58 

34 

710 

676 

80.70 

49.71 

34 

980 

946 

48.52 

35.94 

34 

700 

666 

82.61 

50.43 

34 

970 

936 

49.24 

36.31 

34 

690 

656 

84.58 

51.16 

34 

960 

926 

49.98 

36.69 

34 

680 

646 

86.61 

61.92 

34 

950 

916 

50.74 

37.08 

34 

670 

636 

88.71 

52.70 

34 

940 

906 

51.53 

37.48 

34 

660 

626 

90.88 

53.50 

34 

930 

896 

52.35 

37.89 

34 

650 

616 

93.12 

64.33 

34 

920 

886 

5r20 

38.30 

34 

640 

606 

95.43 

65.18 

34 

910 

876 

54.08 

38.72 

34 

630 

596 

97.81 

66.07 

34 

900 

866 

64.99 

39.15 

34 

620 

586 

100.26 

66.98 

34 

890 

856 

55.93 

39.59 

34 

610 

576 

102.78 

67.92 

34 

880 

846 

56.90 

40.04 

34 

600 

566 

105.37 

68.90 

34 

870 

836 

57.91 

40.51 

34 

590 

556 

108.03 

69.91 

34 

8C0 

826 

58.96 

40.98 

34 

580 

546 

110.76 

60.95 

34 

850 

816 

60.05 

41.47 

34 

570 

636 

113.56 

62.03 

34 

840 

806 

61.18 

41.97 

34 

560 

626 

116.43 

63.15 

34 

830 

796 

62.36 

42.48 

34 

550 

616 

119.37 

64.30 

34 

820 

786 

63.59 

43.00 

34 

540 

506 

122.38 

65.50 

34 

810 

776 

64.87 

43.53 

34 

530 

496 

125.46 

66.75 

34 

800 

766 

66.20 

44.08 

34 

520 

486 

128.61 

68.05 

34 

790 

756 

67.58 

44.65 

34 

510 

476 

131.83 

69.40 

34 

780 

746 

69.01 

45.22  '  34 

500 

466 

135.13 

70.80 

34 

770 

736 

70.50 

45.81  1 

42 


BABIANT  HEAT. 


E 

Table  showing  the  Rate 

OF  Cooling  of 

AN  Incandescent 

Solid  Sphere 

suspended  avithin  a  Cold  Exclosvre. 

i 

i- 

o        5? 

3 

a 

i- 

o       ?J 

o 

gJ 

S.S 

S-a  S? 

"i 

ts 

a§ 

Or-J    M 

.&•& 

5& 
a-i 

P'g'o, 
^  ^^  ^ 

•Ill 

S.S.S 
o 

'i'i 

3& 

Hi 

III 

g;  teg 

1^ 

P4 

1^ 

o 

fi 

°  Cont. 

°  Cent. 

Seoe. 

Sees. 

°  Cmit. 

"  Cent. 

Sees. 

Sece. 

890 

771.12 

22.18 

21.94 

735 

716.12 

30.63 

26.58 

885 

776.12 

22.39 

22.06 

730 

711.12 

30.99 

26.76 

880 

761.12 

22.61 

22.19 

725 

706.12 

31.36 

26.95 

875 

756.12 

22.83 

22.32 

720 

701.12 

31.73 

27.13 

870 

751.12 

23.05 

22.44 

715 

696.12 

32.11 

27.32 

865 

746.12 

23.27 

22.57 

710 

691.12 

32.49 

27.61 

860 

741.12 

23.49 

22.70 

705 

686.12 

32.87 

27.71 

855 

736.12 

23.73 

22.83 

700 

681.12 

33.26 

27.91 

850 

731.12 

23.96 

22.97 

695 

676.12 

33.65 

28.12 

845 

726.12 

24.20 

23.11 

690 

671.12 

34.05 

28.32 

840 

721.12 

24.44 

23.25 

685 

666.12 

34.45 

28.53 

835 

716.12 

24.69 

23.39 

680 

661.12 

34.86 

28.74 

830 

711.12 

24.94 

23.53 

675 

656.12 

35.27 

28.95 

825 

706.12 

25.20 

23.67 

670 

651.12 

35.69 

29.17 

820 

701.12 

25.46 

23.81 

665 

646.12 

36.11 

29.39 

815 

696.12 

25.73 

23.96 

660 

641.12 

36.54 

29.61 

810 

691.12 

26.00 

24.11 

655 

636.12 

36.98 

29.84 

805 

686.12 

26.28 

24.26 

650 

631.12 

37.42 

30.07 

800 

681.12 

26.56 

24.41 

645 

626.12 

37.87 

30.30 

795 

676.12 

26.84 

24.57 

640 

621.12 

38.32 

30.54 

790 

671.12 

27.13 

24.72 

635 

616.12 

38.78 

30.78 

785 

766.12 

27.42 

24.88 

630 

611.12 

39.24 

31.03 

780 

761.12 

27.71 

25.04 

625 

606.12 

39.71 

31.28 

775 

756.12 

28.01 

25.20 

620 

601.12 

40.19 

31.53 

770 

751.12 

28.31 

25.36 

615 

596.12 

40.67 

31.79 

765 

746.12 

28.62 

25.53 

610 

591.12 

41.16 

32.05 

760 

741.12 

28.93 

25.70 

605 

586.12 

41.65 

32.31 

755 

736.12 

29.25 

25.87 

600 

581.12 

42.15 

32.58 

750 

731.12 

29.58 

26.04 

595 

576.12 

42.66 

32.85 

745 

726.12 

29.92 

26.22 

590 

571.12 

43.18 

33.13    1 

740 

721.12 

30.27 

.    26.40 

585 

566.12 

43.71 

33.42    j 

CHAP.  II.      L'AIU  Alios   AT  lilFFi:i!i:ST  rilMVEUATlUES. 


43 


E 

Table  siiowino  the  Ratk 

OF  Cooling  of 

AN   InCAN 

DESCIiNT 

SOLII 

)    Sl'UEKIC 

SUSl'KXDKl)    WITHIN   A    L'OLU   AWci.OSl'JiJ-:. 

£ 
If 

o 

lis 

"•si 

la 

S  3 

ill 

5     ■" 

2 

Eh 

li 

n 

11 

E  °    . 

is 

HI 
is: 

o 

5 

'Cmt 

'Cent. 

S«ea. 

Stm. 

•On/. 

°Cmt. 

Stet. 

8k». 

580 

561.12 

44.25 

33.71 

425 

406.12 

71.19 

46.08 

575 

556.12 

44.80 

34.01 

420 

401.12 

72.61 

40.03 

670 

551.12 

45.37 

34.31 

415 

396.12 

74.08 

47.20 

665 

646.12 

46.95 

34.61 

410 

391.12 

76.60 

47.78 

660 

541.12 

46.54 

34.92 

405 

386.12 

77.17 

48.37 

555 

636.12 

47.16 

35.24 

400 

381.12 

78.78 

48.98 

660 

531.12 

47.77 

36.56 

395 

376.12 

80.44 

49.60 

645 

520.12 

48.41 

36.89 

390 

371.12 

82.14 

60.24 

640 

521.12 

49.06 

36.22 

385 

366.12 

83.89 

60.90 

535 

616.12 

49.72 

36.56 

380 

361.12 

86.69 

51.58 

630 

611.12 

50.40 

36.91 

376 

356.12 

87.66 

52.27 

625 

500.12 

51.10 

37.26 

370 

351.12 

89.47 

62.98 

620 

601.12 

51.82 

37.62 

365 

346.12 

91.44 

63.71 

515 

496.12 

52.66 

37.99 

360 

341.12 

93.47 

64.46 

610 

491.12 

53.32 

38.36 

365 

336.12 

95.55 

65.23 

505 

486.12 

54.11 

38.74 

350 

331.12 

97.69 

56.02 

600 

481.12 

54.93 

39.13 

345 

326.12 

99.89 

56.84 

495 

476.12 

56.78 

39.63 

340 

321.12 

102.15 

57.68 

490 

471.12 

66.65 

39.94 

335 

316.12 

104.46 

58.66 

486 

466.12 

57.65 

40.35 

330 

311.12 

106.83 

59.46 

480 

461.12 

58.48 

40.77 

325 

306.12 

109.26 

60.37 

475 

466.12 

59.44 

41.20 

320 

301.12 

111.74 

61.32 

470 

451.12 

60.44 

41.64 

315 

296.12 

114.28 

62.30 

465 

446.12 

61.47 

42.10 

310 

291.12 

116.87 

63.31 

460 

441.12 

62.54 

42.66 

306 

286.12 

119.62 

64.36 

465 

436.12 

63.65 

43.03 

300 

281.12 

122.23 

65.44 

450 

431.12 

64.80 

43.51 

296 

276.12 

125.00 

66.56 

445 

426.12 

65.99 

44.00 

290 

271.12 

127.83 

67.72 

440 

421.12 

67.22 

44.50 

285 

266.12 

130.71 

68.92 

435 

416.12 

68.60 

46.01 

280 

261.12 

133.65 

70.62 

430 

411.12 

69.82 

45.64 

275 

256.12 

44  BABIANT  HEAT.  CHAP.  ii. 

tions.  It  vriU  he  seen  that  tlie  time  occupied  in  cooling  tlie 
radiating  sphere  through  a  range  of  ten  degrees  fonns  the 
basis,  the  temperature  being  of  course  deduced  from  the  indi- 
cation of  the  thermometer  /.  The  advocates  of  Dulong  and 
Petit's  doctrine  will  be  surprised  to  find  by  our  tables  that 
the  incandescent  sphere  enclosed  in  a  vacuum  surrounded  by  a 
cooling  medium  maintained  at  a  very  low  temperature,  requires 
upwards  of  twenty  seconds  to  cool  five  degrees  Centigrade, 
^vhile  agreeably  to  Duloug's  formula  the  stated  reduction  of 
intensity  takes  place  during  an  interval  occupying  only  a  very 
small  fraction  of  one  second.  Again,  our  tables  show  that 
the  fall  of  temperature  from  1,600°  F.  to  500°  F.  requires 
the  considei'able  lapse  of  ninety-seven  minutes,  a  fact  ^\hich 
alone  proves  that  the  celebrated  formula  of  Dulong  is  grossly 
eri'oneous. 

We  have  before  adverted  to  the  fact  that  physicists  have 
siq:)posed  that  the  rate  of  cooling  of  a  body  approaching  white 
heat  cannot  be  ascertained  practically,  because  we  possess  no 
reliable  instrument  for  measuring  high  temperatures.  MM. 
Dulong  and  Petit,  apparently  impressed  with  this  idea,  con- 
fined their  researches,  as  before  stated,  to  temperatures  below 
that  of  boiling  mercury,  imagining  that  by  observing  the 
rate  of  cooling  up  to  a  differential  temperature  of  240°  C. 
they  would  be  enabled  to  establish  a  law^  which  would  deter- 
mine radiant  energy  for  all  intensities.  Unfortunately,  phy- 
sicists have  accepted  the  result  of  those  researches,  Dulong's 
formula  being  now  the  guide  which  the  student  is  taught  to 
follow  in  calculating  the  energy  of  radiant  heat.     Probably 


CHA1-.  II.      BAVIATWS  AT  DIFFEUE}iT  TEMPERATURES.  45 

uo  doctrine  iu  physics  has  occasioned  such  serious  miscon- 
ception as  that  propounded  by  MM.  Dulong  and  Petit.  The 
advance  of  every  branch  of  knowledge  connected  with  radiant 
hoiit  has  been  retarded  by  the  adoption  of  their  doctrine 
ren-ardin"-  its  transmission.  Among  other  important  matters, 
the  question  relating  to  the  temperature  of  the  sun  has  be 
come  seriously  entangled  by  its  adoption.  It  has  led  such 
eminent  men  as  Pouillet  to  assume  that  the  emission  of  heat 
at  the  surface  of  the  sun  is  so  rapid  that  the  ascertained  enor- 
mous development  of  300,000  thermal  units  in  a  minute,  on 
one  square  foot,  may  be  accounted  for  by  the  accepted  doc- 
trine, even  supposing  the  temperature  of  the  surface  of  the 
photosphere  to  be  only  1,461°  C.  A  glance  at  the  preceding 
Table  E,  which  is  based  on  actual  trial,  shows  the  velocity  of 
cooling  to  be  so  moderate  at  the  high  temperature  of  890°  C, 

that  the  fall  only  amounts  to  — ^  X  (890  -  885)  =  13.5°  C. 
•^  22.18 

in  one  minute,  instead  of  1,870.6°  C.  for  the  stated  tempera- 
ture, shown  by  Dulong  and  Petit's  formula  \'  =  2.037  (1.0077' 
—  1).  It  is  sui-prising  that  the  tme  character  of  this  pal- 
pably erroneous  foi-mula,  so  often  applied  by  engineei-s  and 
physicists,  has  never  been  subjected  to  practical  investigation. 
A  positive  test  might  have  been  applied  in  vaiiuus  ^vays, 
although  not  with  that  degree  of  exactness  which  is  attain- 
able by  the  means  we  have  just  described.  The  fallacy  of 
the  assumption,  that  an  increase  of  a  few  hundred  degrees 
of  temperature  suffices  to  augment  the  rate  of  cooling  a  thou- 
sand fold,  becomes  self-evident  if  \ve  consider  that  an  increased 


46  RADIANT  HEAT.  chap.  ii. 

rate  of  cooliug  menus  u  proportionate  increase  of  the  capabi- 
lity of  commuuicating  mecliauical  energy.  Practical  engineers 
who  have  observed  the  short  time  required  to  raise  a  mass 
of  red-hot  metal  to  the  melting  point,  are  familiar  with  the 
fact  that  the  heat  imparted  to  the  metal  by  the  combustibles 
during  the  short  interval  necessary  to  reach  the  point  of  fusion, 
from  that  of  red  heat,  is  wholly  insufficient  to  communicate 
the  enormous  amount  of  energy  assumed  by  those  who  accept 
MM.  Duloug  and  Petit's  formula.  This  practical  mode  of  test- 
ing the  correctness  of  the  accejjted  doctrine  demands  serious 
reflection.  Let  us  consider  that  bright-red  heat  indicates  a 
temperature  of  1,000°  C,  while  welding  or  white  heat  indi- 
cates 1,500°  C.  Now,  according  to  the  formula  V  =  2.037 
(1.0077'-  1),  the  velocity  of  cooling  at  1,000°  is  represented 
by  a  fall  of  temperature  of  one  degree  in  the  short  time  of 

— -— -  of  a  minute,  while  the  velocity  of  coolius;  at  1,500°  C, 
4,356  J  fc.  )  ' 

assigned  by  the  same  formula,  will  be  at  the  rate  of  one  de- 
gree in  the  exceedingly  brief  period  of  of  a  minute  ; 

^  ^  -^  ^  202,710 

hence  the  energy  imparted  to  the  heated  metal  ^\\n\e  its  tem- 
perature is  being  raised  from  1,000'  to  1,500° — viz.,  500°  C. — 

.,,  ,      202,710 
will  be  "yrrr"  =  46  times  greater  than  the  energy  imparted 

during  the  longer  period  required  to  attain  bright-red  heat. 
Let  us  also  consider  that,  owing  to  the  diminished  differential 
temperature  between  the  burning  combustible  and  the  metal, 
the  latter  will  absorb  proportionably  less  heat  from  the  former 
while  attaining  white  heat  than  before  red  heat  is  reached; 


CHAP.  n.      nADTATTOy  AT  DIFFERENT  TEMPEliATURES.  47 

thus  the  fallacy  of  the  formula  becomes  yet  more  apparent. 
A\"e  have  already  stated  that  the  rate  of  cooling  at  high  tem- 
peratures may  be  determined  with  perfect  accuracy,  by  mea- 
suring the  number  of  therin;il  units  wliich  a  certain  amount 
of  radiating  surface  develops  in  a  given  time.  It  will  be 
shown  in  Chapter  XIII.  that  fused  iron  maintained  at  a  tem- 
peratuie  of  2,940°  F.  above  the  surrounding  air,  develops 
I.oi;]  tliernial  units  per  minute  u^Km  an  area  of  one  square 
foot ;  the  means  employed  to  ascertain  this  fact  being  a  calo- 
rimeter floating  on  the  surface  of  the  fused  metal,  nearly  in 
contact  with  the  same.  -The  illustration  shown  on  Plate  6, 
Fig.  6,  represents  a  vertical  section  of  a  calorimeter  for  mea- 
suring the  radiant  enei'gy  of  incandescent  metals.  It  is  placed 
on  the  top  of  a  block  of  cast  iron  brought  to  white  heat,  in 
an  air-furnace,  the  bottom  of  the  instrument  being  nearly  in 
contact  with  the  top  of  the  incandescent  metal.  The  nature 
of  the  device,  and  the  mode  of  conducting  the  experiment, 
being  precisely  the  same  as  shown  with  great  minuteness  in 
Chapter  XIII.,  it  w  ill  only  be  necessary  to  observe,  with  refe- 
rence to  the  apparently  improtected  condition  of  the  heater, 
that  the  initial  temperatiire  of  the  water  contained  in  the  same 
is  equal  to  the  atmospheric  temperature,  while  the  powerf'ul 
radiation  from  the  incandescent  block,  together  with  the  inter- 
vention of  the  double  casing,  effectually  prevents  cooling  l)y 
external  cuirents  of  air.  Again,  the  duration  of  the  exi^eri- 
ments  being  restricted  to  a  few  minutes,  the  refrigerating  in- 
fluence of  the  surrounding  air  will  be  practically  inappreciable. 
The  result  of  luimerous  experiments  conducted  in  order  to 


48  RADIANT  HEAT.  chap.  il. 

ascertain  the  amount  of  I'adiant  energy  developed  at  various 
differential  tenaperatures  from  100°  F.  to  2,900°  F.,  will  be 
found  by  inspecting  the  annexed  Table  F,  which  shows  the 
number  of  thermal  units  developed  in  one  minute  by  a  radi- 
ating surface  of  one  square  foot.  The  ordinates  of  the  curves 
<i  I)  (see  diagrams  Fig.  7  and  Fig.  8  attached  to  the  illustra- 
tion Plate  7)  rejjresent  the  radiant  energy  developed  by 
the  differential  temperatures  marked  on  the  vertical  base-line 
upon  which  the  ordinates  have  been  projected.  It  should  be 
stated  that  the  thermal  units  represented  by  the  ordinates 
in  Fig.  7  correspond  with  the  energy  developed  by  raising 
the  temperatxire  of  a  quantity  of  water  weighing  1  lb.  avoir- 
dupois 1°  F. ;  while  the  units  ("  caloris ")  expressed  by  the 
ordinates  in  Fig.  8  correspond  with  the  energy  developed  by 
I'aising  the  temperature  of  1  kilogramme  of  water  1°  Centi- 
grade. The  spaces  between  the  ordinates  Fig.  8,  of  course, 
mark  intervals  of  100"  Centigrade,  the  spaces  between  the 
ordinates  in  Fig.  7  marking  intervals  of  100°  Fahrenheit. 
Referring  to  Table  F,  it  mil  be  seen  that  the  number  of 
thermal  units  entered  in  the  third  column  is  that  develojied 
during  one  minute  on  an  area  of  one  square  foot ;  the  cor- 
responding temperature  of  the  radiating  body  being  entered 
in  the  second  column.  The  fourth  column  shows  the  incre- 
ment of  dynamic  energy  for  each  100°  increase  of  tempera- 
ture, also  exj)ressed  in  thei-mal  units.  The  fifth  column  con- 
tains the  rate  of  increment,  assuming  the  minimum  energy 
as  unit.  Eegarding  the  diagrams  Figs.  7  and  8,  let  us  clearly 
understand  that  the  length  of  the  ordinates  of   the  curves  a 


CHAP.  II.      EAI'IATIOX  AT  DIFFERENT  TEMPERATURES. 


4t) 


Ti^ 

Table  showing  teie  Mechanic 

AL  Energy  developed  by 

x' 

11a  1)1  A  XT    I 

E.\T  AT    DII'FEIIENT  INTENSITIES. 

t*  ho 
=  a 

g| 

i  i 

It 
51 

(5 

£P.S 

c  a.'-' 
"3  II 

a 

£  c  3 

—  ■>->. 

c  w^ 

I'M 

1  = 

£'3 

^  1 

it 

c  — 
1  o 

ti 

(5 

ll 
Vi 

^o  —  c: 

>   3   ° 

c  - 

i 

.2  a-" 

a 

E-S  c 

e  E  = 

C.2  = 

4.-5  £ 
■5  E  5 

•Fah. 

•  Fah. 

Thermal 
unite. 

T^aMo. 

'Fah. 

•FcA. 

Thermal 
vniti. 

Thermal 
uniU. 

nat4o. 

CO 

2900 

980.2 

81.7 

12.38 

60 

1500 

209.5 

27.9 

4.22 

CO 

2800 

898.5 

77.2 

11.70 

CO 

1400 

181.6 

25.0 

3.79 

CO 

2700 

821.3 

72.8 

11.03 

60 

1300 

156.6 

22.3 

3.38 

CO 

2600 

748.5 

68.5 

10.38 

60 

1200 

134.3 

19.8 

3.00 

CO 

2500 

680.0 

64.3 

9.74 

60 

1100 

114.5 

17.5 

2.65 

CO 

2400 

615.7 

60.2 

9.12 

CO 

1000 

97.0 

15.4 

2.33 

CO 

2300 

555.5 

56.2 

8.51 

CO 

900 

81.6 

13.5 

2.05 

60 

2200 

499.3 

52.3 

7.92 

60 

800 

68.1 

11.8 

1.79 

60 

2100 

447.0 

48.5 

7.35 

60 

700 

56.3 

10.3 

1.5C 

60 

2000 

398.5 

44.8 

6.79 

60 

COO 

46.0 

9.1 

1.38 

60 

1900 

353.7 

41.2 

6.24 

60 

500 

36.9 

8.2 

1.24 

60 

1800 

312.5 

37.7 

5.71 

CO 

400 

28.7 

7.6 

1.15 

CO 

1700 

274.8 

34.3 

5.20 

CO 

300 

21.1 

7.3 

1.10 

60 

1600 

240.5 

31.0 

4.70 

CO 
CO 

200 
100 

18.8 
6.6 

7.2 

1.09 

•  Cct 

tiffrade. 

*  Centigrade. 

15 

1600 

242.9 

36.0 

11.61 

15 

800 

48.5 

11.3 

3.64 

15 

1500 

206.9 

32.1 

10.35 

15 

700 

.  37.2 

9.3 

3.00 

15 

1400 

174.8 

28.8 

9.29 

15 

600 

27.9 

7.4 

2.39 

15 

1300 

14C.0 

25.5 

8.22 

15 

500 

•  20.5 

5.7 

1.84 

!    15 

1200 

120.5 

22.3 

7.19 

15 

400 

14.8 

4.C 

1.48 

15 

1100 

98.2 

19.5 

6.29 

15 

300 

10.2 

3.7 

1.19 

1   ^^ 

1000 

78.7 

16.4 

5.29 

15 

200 

6.5 

3.4 

1.09 

1   15 

900 

62.3 

13.8 

4.46 

15 

100 

3.1 

50  RADIANT  HEAT.  chap.  ii. 

b  represent  the  nuiii];er  of  thermal  units  actually  transferred 
from  one  square  foot  of  radiating  surface  to  the  fluid  con- 
tained in  the  calorimeter,  during  one  minute,  the  temjjerature 
of  the  radiator  being  that  marked  on  the  vertical  line.  It 
should  be  particularly  noticed  that,  while  the  energy  trans- 
ferred at  100°  C.  is  3.1  thermal  units  (caloris),  see  Table  F, 
it  amounts  to  242.9  such  units  at  1,600°  C. ;  hence  the  energy 

242.9 
•vvill  be  -; — —  =  78.3    times   greater  at   a   differential  "tempe- 
3.1 

rature   of    1,600°   C.   than  at   100°   C.      Newton's    law   shows 

that  the  radiant  energy  augments  in  the  ratio  of  1,600  :  100 

=  16  :  1.     It  will  thus   be  seen  that  the  actual    increase  of 

7o.O  ,  .  -  •  T       1 

energy  is  =    4.89  times  greater  tlian  that  assigned    by 

the  doctrine  the  correctness  of  which  our  investigations  tend 
to  prove.  The  fact  should  not  be  overlooked  that  the  stated 
discrepancy  refers  to  the  maximum  intensity  of  overheated 
fused  cast  iron  just  before  the  internal  molecular  arrangement 
is  broken  up  and  the  metal  dissipated.  Besides,  we  have 
already  pointed  out  that  the  expansion  of  metals  is  accompa- 
nied by  molecular  change  within  the  mass,  augmenting  the 
energy  of  radiation.  Nor  should  the  fact  be  lost  sight  of 
that  Newton's  doctrine  takes  no  cognizance  of  such  mole- 
cular change  or  disturbance  within  the  heated  body.  The 
insignificance  of  the  apparent  error  of  the  Newtonian  law 
referred  to  will  be  seen  by  a  practical  application  of  the 
rival  theory  of  MM.  Dulong  and  Petit.  Let  us  compare 
the  difference  of  energy  produced  at  the  extremes  of  100°  C. 


CHAP.  II.      UADIATIOX  AT  l)ll-FEliEyT  TEMPERATURES.  •''1 

and  1,500°  C.  ditferential  temperature  established  by  their  re- 
searches. According  to  the  tables,  accepted  by  Prof.  Stewart 
and  others,  contained  in  the  second  part  of  Duloug  and  Petit's 
famous  \\  ork,  "  The  Laws  of  Refrigeration,"  the  rate  of  co(.)l- 
ing  at  a  differential  temperature  of  100^  C.  is  2°.30  C.  in 
one  minute  (the  surrounding  medium  being  maintained  at 
the  freezing  point  of  water) ;  while  at  a  differential  tempe- 
rature of  240°  C.  the  rate  is  stated  to  be  10°.()9  C.  Applying 
these  rates  to  the  fonnula  of  Dulong  and  Petit,  it  will  be 
found  that  when  the  differential  temperature  is  1,500°  C.  the 
fall  will  be  202,710°  C.  in  one  minute.     The  radiant  energy 

202,71(» 
parted  with  at  1,500°  C.  will  accordingly  be  —         ■  =  88,1 3y 

times  greater  than  at  100  C.  But  our  tables  and  diagrams, 
based  on  actual  trial,  show  that  the  radiant  energy  at  1,500'  C. 

is  only  - — '—  =  66.7  times  greater  than  at  100°  C.     Hence  the 

radiant  energy  at  1,500°  C,  agreeably  to  Dulong  and  Petit's 

theoiT,  will  l)e  — '——  =  1,321  times  higher  than  that  estab- 
•''  66.7 

lished  by  our  elaborate  practical  investigation. 


CHAPTER   III. 


INTENSITY  OP  SOLAR  RADIATION. 


The  illusti-iitlon  shown  on  Plate  8  represents  a  vertical 
section  of  an  instrument  constnicted  for  ascertaining,  by  a 
new  and  exact  method,  the  intensity  of  solar  radiation  at  the 
surface  of  the  eai-th,  specially  arranged  for  revolving  obser- 
vatories. Sir  John  Herschel's  definition  of  the  word  actino- 
meter — "  an  instrument  for  measuring  the  intensity  of  heat  in 
the  sun's  rays  " — warrants  the  adoption  of  that  term. 

The  caiises  which  modify  the  intensity  of  solar  radiation 
are  chiefly  :  the  position  of  the  eai-th  in  its  orbit,  the  sun's 
zenith  distance — on  which  depends  the  depth  of  the  atmosjihere 
to  be  penetrated  by  the  rays — and  vapors  in  the  atmosphere. 
The  temperature  of  surrounding  objects  which  radiate  towards 
substances  exposed  to  the  sun's  rays,  and  the  heat  abstracted 
from  such  substances  by  currents  of  air,  present  serious  dis- 
turbing elements,  rendering  an  accui-ate  determination  of  the 
radiant  intensity  by  ordinary  thei'mometers  practically  impos- 
sible.    It  is  haiilly  necessary  to  point   out  that  solar  inten- 


CHAP.  III.  iyTi:NSITy  OF  SOLAR  KADIATION.  5:J 

sity  cannot  be  satisfactorily  ascertaiuetl  by  tlio  old  niethoil 
of  deducting  the  temperature  of  a  thermometer  in  the  .shade 
from  that  of  another  thermometer  exposed  to  the  sun.  The 
investigations  of  Daniell  relating  to  the  sun's  radiant  lu-at, 
fiequently  referred  to  in  works  on  meteorology,  conducted  in 
the  latitude  of  London,  where  the  depth  of  the  atmo.sphere  at 
noon,  during  the  summer  solstice,  is  0.57  greater  than  on  the 
ecliptic,  merit  serious  consideration.  The  subjoined  table  con- 
tains the  result  of  his  observations  on  solar  radiation  through- 
out a  day  in  the  month  of  June. 

A  glance  at  this  table  sLows  that,  according  to  the  adopted 
method  of  determining  the  intensity  of  solar  radiation  by  de- 
ducting the  temperature  indicated  by  a  thermometer  in  the 
shade  from  the  temperature  attained  in  the  sun,  the  ladiant 
heat  is  considerably  less  before  than  after  noon.  The  diffe- 
rential temperature,  or  solar  intensity,  at  9  A.jr.,  according  to 
this  table,  is  25°,  while  at  3  p.ji.,  with  an  equal  zenith  distance 
and  equal  depth  of  atmosphere  to  penetrate,  the  solar  intensity 
is  stated  to  be  62°,  thus  exhibiting  the  enornu)US  difference  of 
27°.  An  explanation  of  the  causes  of  the  extraordinary  errora 
of  Daniell's  table  is  scarcely  needed,  but  attention  should  be 
called  to  the  gross  imperfection  of  such  a  mode  of  detennin- 
infj  solar  radiation  as  that  of  noting  the  different  indications 
of  shaded  and  exposed  theiTnometere.  During  the  early  stages 
of  my  investigation  relating  to  the  mechanical  properties  of 
the  sun's  radiant  heat,  I  adopted  this  mode  of  ascertaining 
the  temperature  produced  by  solar  radiation  ;  but  notwith- 
standing numerous  expedients  lesoited  to  in  order  to  prevent 


54 


BADIANT  UEAT. 


Time  of  obser- 
vation. 

TEMPERATURE,  A.M. 

Differential 

temperatui'e  or  solar 

intensity. 

In  the  sun. 

In  the  shade. 

'Fah. 

°Cmt. 

°  Fah. 

°Cmt. 

'  Fah. 

'  Cent. 

9.00 

93 

33.88 

68 

20.00 

25 

13.88 

9.30 

103 

39.44 

69 

20.55 

34 

18.89 

10.00 

111 

43.88 

70 

21.11 

41 

22.77 

10.30 

119 

48.33 

71 

21.66 

48 

26.67 

11.00 

124 

SI. 11 

71 

21.66 

53 

29.45 

11.30 

125 

51.66 

72 

22.21 

53 

29.45 

12.00 

129 

53.88 

73 

22.77 

56 

31.11 

1. 

°   0 

«H  .2 

TEMPERATURE,  P.M. 

Differential 

temperature  or  solar 

intensity. 

In  the  sun. 

In  the  shade. 

'Fah. 

°  Cent. 

'Fah. 

°Omi. 

'Fah. 

°  Cent. 

12.30 

132 

55.55 

74 

23.33 

58 

32.22 

1.00 

141 

60.55 

74 

23.33 

67 

37.22 

1.30 

140 

60.00 

75 

23.88 

65 

36.12 

2.00 

143 

61.66 

75 

23.88 

68 

37.78 

2.30 

138 

58.88 

76 

24.44 

62 

34.44 

3.00 

138 

58.88 

76 

24.44 

62 

34.44 

3.30 

132 

55.55 

77 

25.00 

55 

30.55 

4.00 

124 

51.11 

76 

24.44 

48 

26.67 

4.30 

123 

50.55 

77 

25.00 

46 

25.55 

5.00 

112 

44.44 

76 

24.44 

36 

20.00 

5.30 

106 

41.11 

75 

23.88 

31 

17.23 

6.00 

100 

i 

37.77 

73 

22.77 

27 

15.00 

CHAP.  in.  INTEXSITT  OF  SOLAR  RADIATION.  55 

the  thermometers  from  being  unduly  influenced  by  the  I'adiant 
beat  of  the  air  and  surrounding  objects,  I  failed  to  .secure 
satisfactory  results.  The  most  important  point — the  ctjntml- 
ling  the  irregular  action  of  the  surrounding  air,  wliirli  ;itl'crt> 
the  exposed  as  well  as  the  shaded  thermometer — having  pre- 
sented obstacles  which  no  mechanical  airangement  whatever 
could  overcome,  I  adopted  the  method  of  wholly  excluding 
the  atmosphere.  By  this  expedient  the  bull)  of  the  thermo- 
meter within  the  instiniment  becomes  surrounded  by  ether 
only ;  hence  the  energy  transmitted  by  the  sun's  rays  deter- 
mines the  temperature  freed  from  atmospheric  influence.  It 
will  be  objected  that  the  thermometer  cannot  be  applied 
within  a  vacuum  without  the  employment  of  some  transpa- 
rent covering,  and  that,  conseqixently,  the  energy  of  the  rays 
will  suffer  considerable  loss  before  reaching  the  bulb.  This 
objection  is  readily  met  by  applying  a  thin  lens  of  about  50 
ins.  focus,  inserted  at  such  a  distance  tVom  the  bulb  that  the 
gain  effected  by  concentrating  the  rays  will  exactly  balance 
the  loss  of  calorific  energy  attending  their  passage  through 
the  lens.  It  is  evident,  however,  that  a  plane  crystal  might 
be  employed  in  place  of  the  lens,  provided  its  al)Sorptive 
power  were  known.  I  have  accordingly  constnicted  an  appa- 
ratus for  measuring  the  loss  of  calorific  energy  attending  the 
passage  of  the  sun's  rays  through  plane  crystals  of  adequate 
thickness  to  resist  the  atmospheric  pressure  when  the  air  is 
withdrawn  from  the  interior  chamber  of  the  instrument.  It 
should  be  mentioned  that  many  of  the  observations  recorded 
in  this  work  have  been  made  with  an  actinometer  provided 


56  BADIAXT  HEAT.  CHAP.  ill. 

with  a  plane  crystal,  tlie  absorptive  power  of  wliicli  amounts 
to  0.066.  Veiy  little  trouble  has  been  experienced  in  record- 
ing observations  made  with  this  instrument,  the  indicated  dif- 
ferential temperatures  having  simply  been  multiplied  by  the 
coefficient  1.066. 

Careful  inspection  of  our  illustration,  together  with  the 
foregoing  explanations  regarding  the  nature  of  the  lens  and 
its  substitute,  and  the  object  of  applying  the  recording  ther- 
mometer within  a  vacuum,  render  a  minute  description  of  the 
detail  of  the  device  unnecessary.  Like  the  solar  calorimeter, 
Plate  10,  particularly  described  in  Chapter  V.,  the  actino- 
meter  is  attached  to  a  table,  the  face  of  which  is  kept  per- 
pendicular to  the  sun  during  observations.  It  is  also  provided 
with  a  graduated  arc  and  stationary  index,  similar  to  those 
applied  to  the  solar  calorimeter,  by  means  of  which  the  sun's 
zenith  distance  may  be  ascertained  at  every  instant.  The 
chamber  containing  the  bulb  of  the  thermometer  is  4f  ins. 
in  diameter,  plated  with  polished  nickel  and  surrounded  with 
a  double  casing,  through  which  a  current  of  water  is  circu- 
lated by  means  precisely  like  those  employed  in  the  solar 
calorimeter,  the  vacuum  being  also  produced  in  a  similar 
manner,  and  flexible  tubes  employed  for  connecting  the  in- 
strument with  the  stationary  pump.  The  cistern  which  sup- 
plies the  circulating  water  is  kept  at  a  constant  tempera- 
ture of  60°  F.,  and,  in  order  to  secure  perfect  accuracy,  the 
thermometer  employed  for  regulating  this  temperature  is  so 
applied  that  the  return  current  from  the  actinometer  to  the 
cistern  circulates  round  its  bulb.     A  thin   metallic  screen  of 


CHAP.  in.  INTEXSITV  OF  SOLAh'  i:.\l>IATI<)X.  5'! 

aiimilar  form,  supported  by  four  columus,  and  plated  witli 
silver,  protects  the  instrument  from  the  sun's  radiant  heat, 
for  the  puqiose  of  economizing  the  cooling  medium  required 
to  keep  the  circulating  water  at  tlie  proper  temperature. 
The  opening  in  the  screen  corresponds  with  the  size  of  the 
lens.  The  bulb  of  the  thermometer  is  3  ins.  in  length,  in 
order  to  expose  a  relatively  large  surface  to  the  action  of 
the  solar  rays  ;  the  proportion  of  heating  surface  to  the  con- 
tents of  the  bulb  being  thus  much  greater  than  in  ordinary 
thermometers.  The  upper  half  of  the  bulb  is  coated  with 
l;iiii2)ldack,  the  lower  half  being  exposed  to  the  action  of 
the  reflected  raya  fi'om  the  bottom  of  the  chamber,  in  such 
a  manner  that  the  radiation  of  this  lower  bright  half  of  the 
bulb  is  neutralized  by  reflected  heat.  Much  pains  has  been 
bestowed  in  order  to  attain  this  desirable  object.  Before 
making  an  observation  with  the  actinometer,  the  vacuum 
gauge  should  be  inspected,  and  the  water  from  the  cistern 
be  permitted  to  run  freely  throxigh  the.  casing  for  several 
minutes  until  the  temperature  of  the  return  current  an<l  that 
indicated  by  the  enclosed  thermometer  correspond.  The  ob- 
servatory being  then  turned  to  the  sun,  and  the  declination 
table  on  which  the  actinometer  stands  adjusted  to  the  proper 
angle,  the  cover  over  the  lens  should  be  removed.  The 
height  of  the  mercurial  column  of  the  enclosed  thermometer 
will  then,  in  due  time,  indicate  Avith  absolute  certainty  the 
intensity  of  the  sun's  radiant  heat,  independent  of  atmospheric 
temperature  and  other  disturbing  causes  which  lender  the 
indications  of  solar  intensity  by  common  thermometers  mere 


58  RADIANT  MEAT.  chap.  hi. 

approximations.  It  will  be  evident  that,  since  the  instru- 
ment is  kept  at  a  constant  temperature  of  60°,  it  continually 
radiates  heat  of  that  intensity  towards  the  bulb  of  the  en- 
closed thermometer ;  hence  the  zero  of  the  thermoraetric 
scale  of  the  actlnoraeter  will  mark  60°  above  Fahrenheit's 
zero.  Obviously,  the  point  reached  by  the  mercurial  column 
of  the  enclosed  thermometer  above  the  stated  zero  on  expo- 
sure to  the  sun's  rays  can  only  be  attained  in  virtue  of  the 
power  of  unaided  solar  radiation.  In  supjiort  of  this  asser- 
tion it  may  be  well  to  repeat  the  explanation  already  given, 
namely,  that  the  bulb  is  surrounded  by  ether  alone,  freed 
fi'om  all  disturbing  influences  of  ponderous  matter,  and  that 
the  heat  which  determines  the  zero  of  the  actinometer  is  sup- 
plied by  radiation  from  the  instalment  itself.  The  important 
question  of  actual  intensity  with  reference  to  the  adopted 
"  absolute  "  zero  will  be  discussed  in  Chapters  IX.  and  XVI. ; 
but  it  may  be  well  to  state  in  this  place  that  the  actino- 
meter merely  shows  the  thermometric  interval  of  solar  inten- 
sity on  Fahrenheit's  scale,  without  reference  to  the  position 
of  that  interval  on  a  scale  which  commences  at  the  accepted 
"  absolute  zero."  I  regard  this  absolute  zero,  however,  as  an 
ignis-fatvv8,  retreating  as  fast  as  we  approach  it. 

It  should  be  observed  that  all  the  actinometric  observa- 
tions contained  in  this  work  have  been  made  in  lat.  40  deg. 
42  min.,  thus  only  17  deg.  12  min.  from  the  trojjic  of  Cancer. 
The  depth  of  atmosphere  so  near  the  tropics  being,  at  mid- 
summer, only  0.047  greater  than  on  the  ecliptic,  while  the 
sun's  zenith  distance  on  lat.  40  dea:.  42  min.  duriuc  the  winter 


CHAP.  III.  lA'TEXSITl'  OF  SOLAR  HADIATION.  59 

solstice  is  only  2  cleg.  18  min.  less  thau  at  the  pole  at  mid- 
summer, I  have  lieen  enabled  to  determine  the  maximum 
intensity  of  solar  radiation  for  all  latitudes  from  the  equator 
to  the  ])ole.  The  diagram  represented  on  PI.  9,  Fig.  1,  shows 
the  relations  of  atmospheric  depth  and  solar  intensity  for  each 
degree  of  zenith  distance  from  the  vertical  to  the  75th  dei^ree. 
A  brief  description  will  suffice  to  render  this  diagram  readily 
understood.  The  ordinates  between  the  curve  e  a  and  the 
base  line  /  <y  exhibit  the  true  proportions  of  the  depth  of  the 
atmosphere  penetrated  by  the  rays  from  the  vertical  to  75  deg. 
zenith  distance  ;  while  the  ordinates  of  the  curve  c  a  indi- 
cate tlie  relative  intensity  of  the  sun's  I'adiaut  heat  at  the 
summer  solstice  for  each  degree  of  the  sun's  zenith  distance 
from  the  vertical  to  75  deg.  The  straight  line  bah  the 
tangent  of  the  cuives  e  a  and  c  a.  It  will  be  seen  by  closely 
examining  these  curves,  and  the  ordinates  resting  on  the  base 
line  /  g  (comparing  the  same  with  the  figures  in  the  tables 
of  this  chapter),  that  the  intensities  of  solar  radiation  var}' 
nearly  in  the  inverse  ratio  of  the  cube  roots  of  the  atmospheric 
depth  for  all  zenith  distances  not  exceeding  75  deg.  The  ordi- 
nates between  the  irregular  line  d  d  d  and  the  base  line  /'  <j 
show  the  solar  intensity  for  each  degree  of  zenith  distance 
from  23  deg.  to  75  deg.,  ascertained  by  actinometric  observa- 
tion during  a  day  in  the  month  of  August  when  the  sun  was 
obscured  by  cirri  of  average  density.  AVith  refei-ence  to  the 
solar  engine  this  irregular  line  d  d  d  possesses  great  interest, 
as  it  indicates  the  available  solar  energy,  foi'  mechanical  [lur- 
poses,  during  a  day  A\hen  the  sun  is  partially  obscured. 


60  BABIANT  HEAT.  chap.  hi. 

The  engineer  will  regard,  this  diagram  as  a  solar  indicator- 
card,  the  space  below  the  line  d  d  d  representing  the  avail- 
able power,  while  the  sj)ace  contained  between  that  line  and 
the  curve  c  a  indicates  the  loss.  For  the  purpose  of  elucida- 
tion, the  Xorth  Pole,  together  ^vith  the  cities  of  Edinburgh, 
London,  Paris,  and.  New  York,  have  been  introduced  on  this 
diagram,  their  positions  having  reference  solely  to  the  depth 
of  atmosphere  and  solar  intensity  during  the  summer  solstice. 
The  annexed  Tables  A,  B,  and  C  show  the  relative  de^Jth  of 
atmosphere  and  maximum  solar  intensity  at  midsummer  fiir 
each  degree  of  the  sun's  zenith  distance  from  the  vertical  to 
75  deg. 

Referring  to  the  second  part  of  the  diagram,  it  will  be 
found  that  Fig.  2  contains  a  delineation  of  the  graduated 
plate  specially  mentioned  in  Chapter  V.  This  plate  is  fur- 
nished with  a  movable  radial  index,  to  enable  the  observer 
to  ascertain  quickly  the  depth  of  atmosphere  corresponding 
with  observed  zenith  distances.  The  gradiiated  plate  is  con- 
structed to  a  scale  of  24  miles  to  the  inch,  the  curvature 
of  the  earth's  surface  and  the  atmospheric  boundary  (sup- 
posed to  extend  42  miles  above  the  earth)  being  accurately 
laid  down  according  to  the  said  scale.  The  vei'tical  depth 
of  the  atmosjDhere,  it  will  be  seen,  has  been  divided  into  100 
equal  parts,  the  same  graduation  having  been  introduced  on 
the  movable  index.  Accordingly,  by  placing  this  index  at 
angles  corresponding  with  the  observed  zenith  distance,  the 
intersection  of  its  upper  edge  with  the  top  line  of  the  atmo- 
sphere  will    show   the   proportion    of   diagonal    and    vertical 


IXTEXSITY  OF  SOLA  R  ItA  DIA  TION. 


fil 


A 

TaRLE  SllOWIXG  THE  InTEXSITY  OF 

Solar  U. 

VDIATIOS  ANM)  TUE 

Atmospheric  Depth  for  given  Zenith  Distances. 

Atmospheric 
depth. 

Increment 

of  atmospheric 

deptti. 

Maximum 

intensity. 

Observed  intensity 

during 

a  partially  cloudy  day. 

Dtg. 

Ktlativf. 

Jielallrt. 

•  Fah. 

•Cdiit. 

•Fah. 

•  Cent. 

0 

1.000 

0.000 

67.20 

37.33 

1 

1.000 

0.000 

67.19 

37.33 

2 

1.000 

0.000 

67.18 

37.32 

3 

1.001 

0.001 

67.16 

37.31 

4 

1.002 

0.002 

67.14 

37.30 

5 

1.003 

0.003 

67.11 

37.28 

G 

1.005 

0.005 

67.07 

37.26 

7 

1.007 

0.007 

67.02 

37.24 

8 

1.010 

0.010 

66.97 

37.21 

9 

1.013 

0.013 

66.91 

37.17 

10 

LOIG 

0.016 

66.84 

37.13 

11 

1.019 

0.019 

66.77 

37.09 

12 

1.023 

0.023 

66.69 

37.05 

13 

1.027 

0.027 

66.60 

37.00 

14 

1.031 

0.031 

66.51 

36.95 

15 

1.030 

0.036 

66.41 

36.89 

16 

1.041 

0.041 

66.30 

36.83 

17 

1.046 

0.046 

66.19 

36.77 

18 

1.051 

0.051 

66.07 

36.70 

19 

1.057 

0.057 

65.94 

36.63 

20 

1.063 

0.063 

65.80 

36.56 

21 

1.070 

0.070 

65.66 

36.48 

22 

1.077 

0.077 

65.51 

36. 4C 

23 

1.085 

0.085 

65.36 

36.31 

5 

0.5 

33.05 

24 

1.093 

0.093 

65.20 

36.22 

58.4 

32.44 

25 

1.102 

0.102 

1 

65.03 

36.13 

57.7 

-  32.04 

62 


BABIANT  HEAT. 


B 

Table  siio\vi\g  the  Intensity  of  Solak  Eadiation 

\NI)  THE 

Atmusi'iiekic  Depth  for  given  Zenith  Distances. 

^3 

Atmospheric 
depth. 

Increment 

of  atmospheric 

depth. 

Maximum 

intensity. 

Observed  intensity 

during 

a  partially  cloudy  day. 

Dig. 

Relalviie. 

JielatiTi. 

'  Fah. 

°Cmt. 

°  Fah. 

'CeiU. 

26 

1.111 

0.111 

64.85 

36.03 

58.4 

32.44 

27 

1.121 

0.121 

64.67 

35.93 

57.5 

31.95 

28 

1.132 

0.132 

64.48 

35.82 

57.7 

32.05 

29 

1.141 

0.141 

64.29 

35.72 

57.7 

32.05 

30 

1.152 

0.152 

04.08 

35.60 

57.8 

32.11 

31 

1.104 

0.164 

63.87 

35.49 

56.9 

31.61 

32 

1.176 

0.176 

63.66 

35.36 

56.9 

81.61 

33 

1.189 

0.189 

63.43 

35.24 

56.7 

31.50 

34 

1.203 

0.203 

63.20 

35.11 

57.0 

31.66 

35 

1.217 

0.217 

62.96 

34.98 

56.8 

81.55 

36 

1.232 

0.232 

62.72 

84.84 

56.4 

31.38 

37 

1.248 

0.248 

62.47 

34.70 

56.2 

31.22 

38 

1.265 

0.265 

62.21 

34.56 

55.8 

81.00 

39 

1.283 

0.283 

61.94 

34.21 

56.1 

31.17 

40 

1.302 

0.302 

61.67 

34.26 

55.0 

30.55 

41 

1.322 

0.322 

61.39 

34.11 

54.8 

80.44 

42 

1.342 

0.342 

61.10 

38.95 

54.8 

80.44 

43 

1.363 

0.363 

60.81 

38.78 

54.9 

30.50 

44 

1.884 

0.384 

60.51 

33.62 

54.6 

80.34 

45 

1.406 

0.406 

60.20 

38.45 

54.7 

30.40 

46 

1.431 

0.431 

59.88 

38.27 

54.5 

30.28 

47 

1.457 

0.457 

59.56 

83.09 

54.4 

30.22 

48 

1.485 

0.485 

59.23 

32.91 

53.4 

29.66 

49 

1.514 

0.514 

58.89 

82.72 

53.0 

29.44 

50 

1.545 

0.545 

58.54 

32.52 

58.2 

29.55 

Ii\TE.\SITV  OF  iiOLAh'  KADIATION. 


U3 


c 

Taulk  siio\vix(;  tiii;  In'tkn'sity  of  Solak  U 

VDIATION 

AND  TirE 

Atmospiikuic  Dki'tu  foh  given  Zenith  Distances. 

II 

Atmospheric 
depth. 

Incrempiil 

of  atruospheric 

depth. 

Maximum 

iiUensit)'. 

Obscrve<l  intensity 

during 

a  partially  cloudy  day. 

Dtg. 

lUlatite. 

Belulirt. 

•  Fah. 

•Cent. 

'Fah. 

'Cent. 

51 

1.577 

0.577 

58.18 

32.32 

50.7 

28.16 

5:2 

1.0J2 

0.GJ2 

57.81 

32.12 

50.6 

28.11 

m 

1.648 

0.648 

57.44 

31.91 

45.8 

25.44 

64 

1.686 

0.686 

57.05 

31.70 

45.4 

25.22 

55 

1.726 

0.726 

56.66 

31.48 

44.6 

24.77 

56 

1.769 

0.796 

56.25 

31.25 

44.6 

24.77 

57 

1.815 

0.815 

55.82 

31.02 

47.0 

26.11 

58 

1.864 

0.864 

55.39 

30.77 

48.0 

26.66 

69 

1.916 

0.916 

54.94 

30.52 

47.3 

26.27 

60 

1.970 

0.970 

54.47 

30.26 

47.4 

26.32 

61 

2.037 

1.037 

53.99 

29.99 

46.4 

25.77 

62 

2.098 

1.098 

53.48 

29.72 

46.8 

26.00 

63 

2.164 

1.164 

52.96 

29.42 

4G.S 

26.00 

64 

2.235 

1.235 

52.41 

29.12 

46.4 

25.77 

65 

2.312 

1.312 

51.85 

28.81 

46.1 

25.50 

66 

2.398 

1.398 

51.26 

28.48 

45.0 

25.00 

67 

2.490 

1.490 

60.63 

28.13 

42.6 

23.66 

68 

2.591 

1.591 

49.96 

27.70 

43.1 

23.94 

69 

2.701 

1.701 

49.24 

27.36 

43.2 

24.00 

70 

2.821 

1.821 

48.43 

26.93 

42.8 

23.77 

71 

2.952 

1.952 

47.67 

26.46 

41.9 

23.27 

72 

3.097 

2.097 

46.72 

25.96 

40.4 

22.44 

73 

3.255 

2.255 

45.72 

25.40 

33.5 

18.61 

74 

3.428 

2.428 

44.61 

24.79 

36.3 

20.16 

76 

3.624 

2.624 

43.39 

24.11 

32.4 

18.00 

64  RABIAXT  HEAT.  chap.  hi. 

atmospheric  depth.  The  impoi'taiit  rehntioiis  of  solar  inten- 
sity, zenith  distance,  atmospheric  depth,  and  hititude,  being 
exhibited  by  the  diagram  under  consideration,  let  us  now 
consider  the  mode  adopted  in  constructing  the  same. 

The  data  indispensable  in  constructing  the  curve  c  a,  the 
ordiuates  of  which  represent  the  maximum  solar  intensity  for 
given  zenith  distances  when  the  earth  is  in  aphelion,  first  claim 
our  attention.  It  will  be  perceived,  on  reflection,  that,  owing 
to  the  vai'ying  intensity  resulting  from  change  of  distance  be- 
tween the  sun  and  the  earth,  the  temjierature  produced  by 
solar  radiation  varies  fi'om  day  to  day  with  the  altered  posi- 
tion of  the  earth  in  its  orbit.  Consequently,  observed  defi- 
ciency of  solar  intensity  at  any  given  zenith  distance  does 
not  always  furnish,  as  supposed  by  certain  meteorologists,  a 
correct  indication  of  the  amount  of  absorption  caused  by  the 
presence  of  vapor  in  the  atmosphere.  01)viously,  the  observed 
deficiency  of  intensity  may  result  partially  from  the  earth's 
proximity  to  the  aphelion.  It  will  be  seen  by  reference  to 
Chapter  IV.  that  for  equal  zenith  distance  a  diminution  of 
temperature  of  4°. 66  F.  takes  jilace  during  the  summer  sol- 
stice, compared  with  the  intensity  of  the  radiant  heat  at  mid- 
winter. Consequently,  if  we  omit  to  make  a  proper  allow- 
ance for  the  difference  of  intensity  resulting  from  the  sun's 
distance  at  the  time  of  observation,  no  satisfactory  record  can 
be  produced.  It  is  hardly  necessary  to  point  out  that,  unless 
we  establish  some  fixed  position  of  the  earth  in  its  orbit,  as  a 
zero,  it  will  be  impossible  to  construct  tables  of  varying  solar 
intensity  cajjable  of  being  employed  as  a  means  of  correction. 


OHAi'.  111.  INTENSITY  OF  tSOLAR  RADIATION.  65 

I  have  accordingly  adopted  the  aphelion  as  the  controlling 
zero,  all  my  tables  relating  to  this  subject  having  reference 
to  maadmum  solar  inteimtij  when  the  earth  is  furthest  from 
the  svn.  The  reader  will  iind  the  question  of  solar  distance 
fully  discussed  in  the  next  chapter. 

Regarding  the  observations  which  have  furnished  the  data 
on  which  our  diagram  has  been  constructed  and  the  annexed 
tables  calculated,  it  \\ill  be  necessar)'  to  state,  for  the  infor- 
mation of  those  who  are  not  familiar  with  the  subject,  that 
observations  of  maximum  solar  intensity  should  be  continued 
during  a  series  of  yeai-s.  It  sometimes  happens  that  an  entire 
season  elapses  without  a  single  opportunity  for  a  satisfactory 
observation  presenting  itself.  Records  of  solar  observations 
are  therefore  exceedingly  irregular ;  during  some  seasons  reli- 
able observations  may  be  made  fi'om  day  to  day ;  then  again 
a  considerable  period  intervenes  during  which  the  work  must 
be  wholly  suspended.  Indeed,  the  difficulties  inseparable  from 
investigations  of  maximum  solar  energy  can  hardly  be  exag- 
gerated. A  complete  record  requires  that  the  sun  should  be 
perfectly  clear  while  we  observe  the  temperature  produced 
by  the  rays  for  each  degree  of  the  sun's  zenith  distance,  upon 
each  degree  of  latitude,  for  each  day  in  the  year.  Now, 
observations  continued  during  a  century  would  not  suffice 
to  produce  such  a  record ;  hence  I  have  had  recoui-se  to 
the  graphic  method,  projecting  from  a  base  line  drawn  on  a 
large  diagram  ordinates  representing  the  maximum  intensity 
shown  by  each  satisfactory  observation.  The  position  of  the 
ordinates  thus  projected,  it  is  scarcely  necessarj'^  to  observe, 


66  BADIANT  HEAT.  CHAP.  ill. 

depends  on  the  zenith  distance  under  which  the  respective 
observations  are  made,  while  their  length  will  be  deter- 
mined by  the  observed  maximum  temperature,  to  be  marked 
on  the  diagram  in  accordance  with  a  fixed  scale.  As  the 
recoi'ded  investigations  extend  from  the  vertical  to  V5  deg. 
zenith  distance,  it  will  be  evident  that  the  base  line  should 
be  divided  into  75  equal  parts,  each  division  representing 
one  degree  of  zenith  distance.  Tor  each  successful  observa- 
tion an  ordinate  will  be  projected  at  a  position  on  the  base 
corresponding  with  the  zenith  distance  under  which  the  suc- 
cessful observation  has  been  made  ;  the  length  of  the  ordi- 
nate being  marked  off  according  to  the  fixed  scale  mentioned. 
It  will  be  perceived,  therefore,  that,  at  the  termination  of  a 
series  of  observations,  the  base  line  on  the  diagram,  with  its 
75  equal  divisions,  representing  degrees  of  zenith  distance, 
subdivided  into  minutes,  will  be  studded  with,  a  number  of 
perpendicular  lines  of  unequal  length,  placed  at  irregular  dis- 
tances. In  accordance  with  the  rules  of  the  graphic  system, 
the  terminations  of  the  several  irregularly-spaced  perpendi- 
cular lines  will  then  be  connected  by  a  curved  line  which, 
if  uniform  and  nearly  parabolic  when  completed,  proves  that 
the  observations  have  been  accurate.  Should  it,  however, 
contain  breaks,  or  should  its  curvature  not  be  gradually  in- 
creasing with  increased  zenith  distance,  in  accordance  with 
an  ascending  series,  fresh  observations  must  be  made  at  zenith 
distances  embracing  the  defective  portions.  Again,  it  may 
happen  that  in  connecting  the  terminations  of  the  ordinates 
considerable  gaps  present  themselves ;   in  other  words,  that 


CHAP.  III.  INTENSirV  OF  SOLAE  RADIATION.  C7 

want  of  observatiou  occurs  for  several  succeeding  degrees  of 
zenith  distance.  These  gaps  must  be  filled  by  fresh  observa- 
tions, unless  the  completed  parts  of  the  curve  on  both  sides 
of  the  gap,  when  extended  over  it,  meet  in  such  a  manner  as 
to  produce  a  consistent  curve.  Our  small  diagram  (Plate  9) 
has  been  copied  from  a  large  diagram  constructed  in  accor- 
dance -^vith  the  foregoing  explanation  of  the  plan  adopted. 
The  scale  employed  in  laying  down  the  observed  tempera- 
tures, viz.,  marking  oft"  the  length  of  the  ordinates,  being 
sufiiciently  large  to  admit  of  sho\ving  fractious  of  a  degree 
of  Fahrenheit,  the  temperatures  entered  in  the  Tables  A,  B, 
and  C,  for  given  zenith  distances,  will  be  found  very  pre- 
cise. In  view  of  the  foregoing  explanation  of  the  procedure 
resorted  to,  the  reader  need  not  be  reminded  that  the  tem- 
peratures appearing  in  the  tables  have  not  all  been  deter- 
mined by  actual  observation.  Agreeably  to  the  graphic 
system,  several  of  these  temperatures  have  been  determined 
by  measuring  the  height  of  the  ordinates  in  the  diagram. 
It  needs  no  demonstration,  however,  to  prove  that  intensities 
ascertained  by  measurement,  in  the  manner  pointed  out,  are 
as  reliable  as  if  ascertained  directly  by  the  actinometer,  pro- 
vided the  curve  be  perfect  which  connects  the  termination 
of  the  ordinates  obtained  by  actual  observation.  It  should 
be  stated  that,  during  a  period  embracing  many  yeai-s,  but 
few  favorable  opportunities  have  been  neglected  of  verifying 
the  coiTectness  of  the  preceding  tables.  No  material  discre- 
pancies having  been  obsei-\-ed,  future  investigations  are  not 
likely  to  lead  to  any  important  modifications  of  these  tables. 


68  RADIANT  HEAT.  chap.  hi. 

Possibly  observations  conducted  on  the  table-lands  of  India 
might  show  somewhat  higher  intensities  for  given  zenith  dis- 
tances ;  but  tables  modified  agreeably  to  such  observations 
would  not  be  as  useful  for  meteorological  investigations  con- 
cerning the  effects  of  solar  intensity  in  America  and  Europe 
as  those  here  presented.  It  may  be  mentioned  that  it  was 
my  original  intention  to  extend  the  observations  of  zenith  dis- 
tance and  solar  intensity  from  the  75th  deg.  to  the  horizon; 
l)ut  exjierience  has  shown  that  both  the  eastern  and  western 
horizon,  viewed  fi'om  my  present  observatory,  are  so  seldom 
free  from  clouds  and  haze  that  too  long  a  time  would  elapse 
before  the  investigations  of  atmospheric  absorption  at  extreme 
zenith  distance  could  be  completed.  It  will  be  found,  how- 
ever, on  mature  reflection,  that  the  most  important  meteoro- 
logical phenomena  connected  with  solar  heat  are  confined 
within  the  vertical  segment  of  150  deg.,  which  embi'aces  the 
result  of  my  actinometric  observations. 

With  reference  to  the  maximum  intensity  of  solar  radia- 
tion on  each  degree  of  latitude,  it  will  be  evident  that,  since 
we  jiossess  an  accurate  knowledge  of  the  relation  of  zenith  " 
distance  and  temperature,  we  can  readily  determine  the  maxi- 
mum intensity  for  different  latitudes  during  the  summer  sol- 
stice. For  instance,  we  know,  by  referring  to  the  preceding 
Table  B,  that,  when  the  earth  is  in  aphelion  and  tlie  zenith 
distance  is  43  deg.,  the  temperature  produced  by  solar  radi- 
ation is  60°.81  F. ;  hence  we  know  that  this  temperature 
marks  maximum  solar  intensity  on  the  Arctic  Circle,  the 
latter  being  43  deg.  from    the   ecliptic    at    the    summer  sol- 


INTENSITY  OF  SOL  Alt  RADIATION. 


69 


1 
Table  D,  showing  the 

Temperature  produced  by  8oi,ar  IUdi- 

ATION   AT   NOOX    FOR 

EACH  Degree  of  Latitude  whkn  the 

EaIITH    is    IX    Al'HKLIOX.       NORTHERN    IIeMISPHEIIE. 

Equator 

Lat. 

Solar  intensity  at 
noon. 

Lat. 

Solar  intensity  St 
noon. 

Veg. 

•Fah. 

•Cent. 

Dtg. 

'Fah. 

'  Ctnt. 

0 

65.30 

36.28 

24 

67.20 

37.33 

1 

65.4") 

36.36 

25 

67.19 

37.32 

2 

65.60 

36.44 

26 

67.18 

37.32 

3 

65.75 

36.52 

27 

67.17 

37.31 

4 

65.89 

36.60 

28 

67.14 

37.30 

5 

66.02 

36.68 

29 

67.10 

37.28 

6 

66.15 

36.75 

80 

67.05 

37.25 

7 

66.27 

36.82 

31 

66.99 

37.21 

8 

66.39 

36.88 

32 

66.93 

37.18 

9 

66.49 

36.94 

83 

66.87 

37.15 

10 

66.58 

36.99 

34 

66.80 

37.11 

11 

66.66 

37.03 

35 

66.73 

37.07 

12 

66.73 

37.07 

36 

66.66 

37.03 

13 

66.80 

37.11 

37 

66.58 

36.99 

14 

66.87 

37.15 

38 

66.49 

36.94 

15 

66.93 

37.18 

39 

66.39 

36.88 

16 

66.99 

37.21 

40 

66.27 

36.81 

17 

67.05 

37.25 

41 

66.15 

36.75 

IS 

67.10 

37.28 

42 

66.02 

36.68 

19 

67.14 

37.30 

43 

65.89 

36.60 

20 

67.17 

37.31         44 

65.75 

36.52 

21 

67.18 

37.32    ,    45 

65.60 

36.44 

22 

67.19 

37.32 

46 

65.45 

36.36 

23 

67.20 

37.33 

47 

65.30 

36.28 

Tropic  of  Cancer 

23.30 

97.20 

37.33 

48 

65.13 

36.18 

70 


BABIANT  HEAT. 


Table  E,  SHOwiNa  the  Temperatoke  produced  by  Solar  Kadi- 

ATioN  AT  Noon  for  each  Degree  of  Latitude  when  the 

Eakth  is  in  Aphelion.     Northern  Hemisphere. 

Lat. 

Solar  intensity  at 
noon. 

Lat. 

Solar  intensity  at 
noon. 

Deg. 

'Fall. 

°  Cani. 

Deg. 

°Fah. 

"  Cent. 

49 

64.95 

86.08 

69 

59.76 

33.20 

50 

64.77 

35.98 

70 

59.42 

33.01 

51 

64.58 

35.88 

71 

59.06 

32.81 

Greenwicli 

51.28 

52 

64.48 
64.38 

35.82 
35.77 

72 
73 

58.69 
58.31 

32.61 
32.39 

53 

64.17 

35.65 

74 

57.92 

32.18 

54 

63.96 

35.53 

75 

57.52 

31.95 

55 

63.74 

35.41 

76 

57.10 

31.72 

56 

63.51 

35.28 

77 

56.67 

31.48 

57 

63.28 

35.15 

78 

56.24 

31.24 

58 

63.04 

35.02 

79 

55.79 

30.99 

59 

62.79 

34.88 

80 

55.32 

30.73 

60 

62.53 

34.74 

81 

54.84 

30.46 

61 

62.25 

34.58 

82 

54.35 

30.19 

62 

61.96 

34.42 

83 

53.84 

29.91 

63 

61.65 

34.25 

84 

53.32 

29.62 

64 

61.34 

34.08 

85 

52.78 

29.32 

65 

61.03 

33.91 

86 

52.23 

29.02 

66 

60.72 

33.73 

87 

51.68 

28.71 

Arctic  Circle 

66.30 

60.57 

33.65 

88 

51.11 

28.39 

07 

60.41 

33.56 

89 

50.52 

28.07 

68 

60.09 

33.38 

90 

49.01 

27.73 

CUAP.  III.  INTENSITY  OF  SOLAR  RADIATION.  71 

stice.  Again,  the  North  Pole  being  6C  cleg.  30  rain,  from  the 
ecliptic  at  tlie  same  time,  we  learn,  by  referring  to  Table  C, 
that  the  inaxiinum  solar  intensity  at  the  said  pole  will  be 
y0°.95  F.,  that  being  the  temperature  produced  by  solar  radi- 
ation when  the  zenith  distance  is  GG  dejj.  30  rain. 

The  Tables  D  and  E  contain  the  raaxiniura  solar  intensities 
for  all  latitudes  frora  the  Equator  to  the  North  Pole,  deter- 
mined agreeably  to  the  foregoing  explanation.  The  difference 
of  atmospheric  density  towards  the  pole  calls  for  a  trifling 
correction  of  the  temperature  entered  in  the  table;  but  the 
data  not  being  sufficiently  well  known,  I  have  deemed  it  best 
to  present  the  theoretical  temperatures  without  correction. 

As  far  as  ascertained  by  means  of  the  actinometer,  there 
is  an  appreciable  difference  in  the  sun's  energy  for  corre- 
sponding zenith  distances  early  in  the  morning  and  late  in 
the  afternoon,  which  cannot  be  traced  to  any  adequate  phy- 
sical cause.  I  have  accordingly  attem2:)ted  to  explain  the  dis- 
crepancy on  the  ground  that  the  oi-bital  motion  of  the  earth 
occasions  a  very  considerable  advance  towards,  and  retreat 
from,  the  solar  wave  early  a.m.  and  late  \\y\.  The  subject 
A\ill  be  readily  understood  by  reference  to  Fig.  3,  which 
represents  a  section  of  the  earth  through  the  plane  of  the 
ecliptic,  the  line  d  e  indicating  the  orbit,  and  the  straight 
arrow  the  earth's  course,  while  the  curved  arrow  shows  the 
direction  of  rotation  ;  a  h  c,  etc.,  represent  the  sun's  rays, 
the  orbital  velocity  during  a  definite  period  being  represented 
by/i/  and  h  I.  Let  us  assume  that  the  latitude  of  the  point 
/',  on  the  earth's  surface,  is  such  that  the  prolongation  of  the 


72  RADIANT  HEAT.  chap.  hi. 

ray  ah  to  g  makes  h  g  tliree  times  longer  than  /  g.  It  will 
now  be  evident  ttat  tie  ray  a  li,  AvLicli  lias  been  arrested 
at  h,  must,  while  the  earth  advances  from  /  to  g,  continue  its 
course  at  a  rate  three  times  greater  than  the  earth's  orbital 
velocity,  in  order  to  reach  g  simultaneously  with/".  Assuming 
the  mean  distance  of  the  earth  fi'om  the  sun  to  be  91,430,000 
miles,  the  orbital  velocity  will  be  96,120  ft.  per  second;  hence 
the  ray  a  7i,  to  keep  up  with  the  retreating  western  quarter 


of  the  globe,  must  move  at  the  rate  of  288,360  ft.  per  second. 
The  advancing  eastern  quarter  obviously  imparts  a  retrograde 
movement  to  the  solar  wave,  consequently  the  ray  m  I  will, 
on  grounds  already  set  forth,  be  pushed  towards  the  sun  at 
the  rate  of  288,360  ft.  per  second.  We  have  thus  established 
a  difference  of  advancing  and  retreating  velocity  exceeding 
600,000  ft.  per  second  for  the  lower  altitudes,  which  unques- 
tionably interferes  with  the  regularity  of  the  solar  wave,  and 
thereby  tends  to  disturb  the  uniformity  of  the  intensity  of  the 
sun's  radiant  heat  toAvards  evenino-.   Meteorolo2:ists  will  account 


CHAP.  III.  INTEXSITY  OF  SOLAIi  RADIATION.  73 

for  the  observed  diiniiiution  by  pointing  to  the  fact  that  during 
sunshine — without  wliich  the  actinometer  cannot  be  used — 
the  atmosphere,  in  most  localities,  gradually  becomes  charged 
with  vapor  as  the  day  advances ;  and  that  dust  and  other 
light  dry  particles  are  carried  up  into  the  atmosphere  by  the 
ascending  heated  current  of  air,  thus  obstructing  the  sun's 
rays.  These  plausible  reasons  lose  their  force  if  we  consider 
that,  during  the  season  most  favorable  for  actinometric  obser- 
vations, the  vapors  are  held  fast  within  icy  boundaries,  and 
that  the  dust  is  buried  under  the  snow. 

The  extraordinary  velocity  of  light — nearly  1,700  times 
greater  than  the  velocity  shown  by  the  foregoing  demonstra- 
tion— will  be  urged  as  a  reason  why  the  disturbance  of  the 
solar  wave  could  not  be  practically  appreciable.  This  objec- 
tion cannot  be  deemed  valid  unless  it  can  be  shown  that  the 
dynamic  energy  imparted  by  solar  heat  is  not  partially  the 
result  of  arresting  the  motion  of  the  rays.  The  following 
facts  connected  with  the  subject  demand  serious  considera- 
tion. Owing  to  the  orl)ital  motion  of  the  earth,  the  lens  of 
a  solar  calorimeter,  while  exposed  to  the  radiant  heat,  sweeps 
across  the  path  of  the  sun's  rays  at  the  rate  of  96,120  ft. 
per  second  ;  hence  the  fluid  contained  within  the  insti-ument 
receives  the  energy  of  a  countless  number  of  rays  following 
each  other  in  an  inconceivably  rapid  succession. 

Pouillet,  having  ascei-tained  the  number  of  thermal  units 
imparted  to  the  water  in  his  pyrlieliometer  of  ."^.93  ins.  dia- 
meter, imagined  that  he  had  measured  only  the  energy  of 
the  rays  contained  in  a  pencil  of  11.9  square  inches  section; 


74  BABIANT  HEAT.  chap.  hi. 

whereas,  in  reality,  lie  had,  at  the  end  of  his  experiment  of 
five  minutes'  duration,  subjected  his  instrument  to  the  action 
of  the  entire  number  of  rays  contained  in  a  passing  pencil  or 
sunbeam,  the  section  of  wliich  we  ascertain  by  multiplying  the 
orbital  advance  of  the  earth  during  five  minutes,  28,836,000  ft., 
by  the  diameter  of  the  pyrheliometer,  0.305  ft. 


CHAPTER    IV. 


PERIODIC  VARIATION  OF  THE  INTENSITY  OF  SOLAR 
RADIATION. 


The  preceding  cliapter  has  made  the  reader  familiar  with 
the  construction  of  the  aetinometer,  and  with  the  leading 
results  of  the  investigations  conducted  by  means  of  that  in- 
strument, relating  to  the  variations  of  temperature  consequent 
on  the  sun's  vaiying  zenith  distance.  Let  us  now  con.sider 
the  variation  of  solar  intensity  consequent  on  the  varying 
distance  between  the  sun  and  the  earth  from  day  to  day. 
Meteorologists,  in  recording  the  temperature  produced  by 
solar  radiation,  have  hithei-to  taken  no  notice  of  the  position 
of  the  earth  in  its  orliit  at  the  time  of  making  their  obser- 
vations. At  the  commencement  of  my  investigation  of  the 
mechanical  properties  of  solar  heat,  I  committed  the  same 
oversight ;  but  finding  that  the  result  of  my  observ'-ations  fre- 
quently presented  discrepancies  that  coidd  not  be  accounted 
for  on  the  gi'ound  of  diiferent  zenith  distance  and  presence 
of  vapor  in  the  atmosphere,  I  was  led  to  examine  systema- 
ticall\-   and  very  oaiefuljy  the   effect  on   solar  intensity  pro- 


t6  BABIANT  HEAT.  chap.  iv. 

ducecl  by  tlie  variation  of  the  sun's  distance  from  the  earth. 
Sir  John  Herschel,  in  "  Outlines  of  Astronomy,"  says,  regard- 
ing the  eifect  of  the  sun's  varying  distance  :  "  The  angular 
velocity  of  the  earth  in  its  orbit  is  not  uniform,  but  varies 
in  the  inverse  ratio  of  the  square  of  the  sun's  distance — that 
is,  in  the  same  precise  ratio  as  his  heating  power.  The  mo- 
mentary supply  of  heat,  then,  received  by  the  earth  in  eveiy 
point  of  its  orbit  varies  exactly  as  the  momentary  increase 
of  its  longitude ;  from  which  it  obviously  follows  that  equal 
amounts  of  heat  are  received  from  the  sun  in  passing  over 
equal  angles  round  it,  in  whatever  part  of  the  ellijjse  those 
angles  may  be  situated."  As  regards  the  temperature  deve- 
loped by  the  sun  at  different  periods,  the  author  of  the  "  Out- 
lines of  Astronomy"  calculates  that  there  is  a  difference  of 
one-fifteenth ;  but,  in  judging  of  the  effect  of  this  difference  on 
the  tempeiature  produced  by  solar  radiation,  he  says :  "  We 
have  to  consider  as  our  unit,  not  the  number  of  degrees  above 
a  purely  arbitrary  zero  point  (such  as  the  freezing  point  of 
water  or  the  zero  of  Fahrenheit's  scale)  on  which  a  thermometer 
stands  on  a  hot  summer  day,  as  compared  with  a  cold  winter 
one,  but  the  thermometric  interval  between  the  temj)eratures 
it  indicates  in  the  two  cases,  and  that  it  would  indicate  did 
the  sun  not  exist,  which  there  is  good  reason  to  believe  would 
be  at  least  as  low  as  239°  lelow  zero  of  Fahrenheit.  And  as  a 
temperature  of  100°  F.  ahovezevo  is  no  uncommon  one  in  a  fair 
shade  exposure  under  a  sun  nearly  vertical,  we  have  to  take 
one-fifteenth  of  the  sum  of  these  intervals  (339°),  or  23°  F., 
as  the  least  variation  of  tenq)erature  under  such  (.■ircumstances 


CUAP.  IV.     rEliWDW  VARIATION  OF  HOLAE  EADIATION.  77 

wbicli  can  reasonably  be  attributed  to  the  actual  variation  of 
tlie  sun's  distance."  Adopting  the  stated  calculation,  with- 
out reflecting  on  the  erroneous  grounds  ujion  which  it  rests, 
I  introduced  corrections  of  the  obsei"ved  temperatures  accord- 
ing to  the  supposed  augmentation  of  radiant  intensity,  viz., 
23°  F.  when  the  eaiih  is  in  perihelion.  The  application  of 
these  corrections  proved  that  the  discrepancies  in  my  records, 
before  adverted  to,  amounted  to  only  one-fifth  of  that  which, 
agreeably  to  Sir  John  Ilerschel's  theoiy,  ought  to  have  ap- 
peared. Fully  convinced,  however,  that  the  difference  of  solar 
intensity  resulting  from  the  variation  of  distance  between  the 
sun  and  the  earth  was  the  ti-ue  cause  of  the  irregularity  and 
breaks  in  the  curve  which  I  had  constructed  according  to 
the  observed  temperatures,  I  availed  myself  of  eveiy  favor- 
able opportunity  to  ascertain  the  maxinuun  intensity  produced 
during  the  summer  and  winter  solsticcn.  It  will  be  Avell  to 
state,  for  the  information  of  those  who  have  not  paid  special 
attention  to  the  subject,  that  mean  remdts  of  observation  are 
inadmissible  in  records  intended  to  establish  solar  energy. 
The  superior  intensity  ascertained  at  a  single  observation 
will  set  aside  the  result  of  previous  observations  continued 
for  many  years.  It  will  be  well  also  to  correct  the  prevail- 
ing erroneous  supposition  that  solar  intensity  cannot  be  ascer- 
tained during  the  summer  months,  owing  to  vapor  in  the 
atmosphere.  There  are  short  intervals  at  all  seasons  when 
polar  winds  prevail,  during  which  the  sun  is  perfectly  clear. 
Those  who  have  paid  close  attention  to  this  matter  will  say 
that  thev   have  seen  as  brij^ht  a  solar  disc  in  August   as  in 


78  RADIANT  BEAT.  chap.  it. 

January.  This  fact  has  heen  repeatedly  verified  by  the  indi- 
cations of  my  sohir  calorimeter,  an  unerring  test,  since  it 
records  the  number  of  units  of  heat  developed  by  the  sun 
in  a  given  time  on  a  given  area.  Obviously  the  smallest 
increase  of  the  absoi-ptive  power  of  the  atmosphere  will  be 
detected  by  this  method.  It  will  be  perceived  from  the  fore- 
going remarks  that  the  records  of  solar  intensity  connected 
with  the  solstices,  kept  during  a  series  of  years,  possess  no 
matei'ial  interest  regarding  the  question  at  issue — namely,  the 
true  maximum  difference  of  intensity  of  solar  radiation  when 
the  earth  is  in  aphelion  and  in  perihelion.  The  reader,  there- 
fore, instead  of  being  called  upon  to  examine  an  extended 
record  of  observations,  will  simply  have  his  attention  directed 
to  the  fact  that  January  7,  1871,  the  earth  being  then,  of 
course,  very  near  perihelion,  the  temperature  produced  by 
solar  radiation,  indicated  by  the  actinometer,  reached  57°.25 
F.  at  noon;  the  zenith  distance  being  63  deg.  15  min.  Re- 
fen-ing  to  the  table  of  temperatures  for  given  zenith  distances 
(Chap.  III.),  it  will  be  seen  that  the  temperature  produced  by 
solar  radiation  when  the  earth  is  in  apJielion  is  52°.84  F.  at 
a  zenith  distance  of  63  deg.  15  min. ;  consequently,  an  aug- 
mentation of  solar  intensity  of  57.25  —  52.84  =  4°.41  F.  takes 
place  when  the  earth  is  in  perihelion.  The  result  of  my  acti- 
nometric  observations,  coiitinued  through  a  series  of  years, 
recorded  in  Chap.  III.,  shows  that  when  the  earth  is  in  aphe- 
lion the  maximum  solar  intensity  on  the  ecliptic  is  67°.20  F. 
The  law  of  inverse  squares  being  true  for  spherical  radiators 
and  for  radiating  circular  discs  subtending  small  angles,  the 


cn.\i>.  IV.     PERIODIC  VAIilATIoy  OF  SOLAR  RADIATION.  79 

stated  iutensity  of  solar  radiation  when  the  earth  is  in  a2)lie- 
lion  enables  us  to  determine  with  absolute  cei-tainty  wliat 
temiDeralure  will  lie  produced  when  the  earth  is  in  perihe- 
lion. The  ratio  of  the  earth's  distance  from  the  sun  at  the 
two  opposite  points  of  the  orbit,  in  aphelion  and  in  perihe- 
lion, being  218.1  :  210.0,  while  the  temperature  produced  by 
solar  radiation  during  the  suininei-  sol.-<tiee,  as  stated,  is  G7°.2 
F.,  the  radiant  iutensity  during  the   winter  solstice  will  be 

218.1'  X  67.2 

=  7l''.86  F.     The  temperature  produced  by  solar 

210.9  ^  ^  -^ 

radiation  at  the  surface  of  the  earth  will  thus,  agreeably  to 
the  laws  which  govern  the  transmission  of  radiant  heat,  be 
71.86  -  67.20  =  4°.66  F.  higher  when  the  earth  is  nearest 
the  sun  than  when  furthest  from  it.  The  aetinometric  obser- 
vation, Jan.  7,  1871,  having  established  a  ditVereiitial  teiiipe- 
ratiu-e  of  4°.41  F.,  it  will  thus  be  seen  that  a  discrepancy 
exists  amounting  to  0°.25  F.  That  is,  the  observed  solar  iu- 
tensity, 57°.25,  Jan.  7,  was  0°.25  less  than  the  calculated  in- 
tensity. A  closer  agreement  between  computed  and  observed 
increment  of  solar  intensity  consequent  on  the  eccentricity  of 
the  earth's  orbit  could  not  reasonably  be  exjiected.  Besides, 
the  record  shows  that,  although  the  sun  was  exce]itionally 
clear  on  the  day  mentioned,  there  was  a  perceptible  mist 
round  the  solar  disc,  indicating  that  the  full  radiant  powei- 
was  not  transmitted  to  the  actinometer.  In  constructing  the 
tables  appended  to  this  chapter  I  have,  therefoi-e,  based  my 
calculations  of  diurnal  variation  of  solar  intensity  on  the  dif- 
ferential temperature,   -4". 06  F.,  determined   by   computations 


80  BADIANT  EEAT.  chap.  iv. 

founded  ou  tlie  distance  of  the  earth  from  the  suu  at  the 
opposite  points  of  the  orbit.  Referring  to  the  tables,  it  ^vill 
be  seen  that  the  maximum  temperature  produced  by  solar 
radiation  has  been  entered  for  each  day  throughout  the  year ; 
also  the  increment  of  solar  intensity  for  each  day,  consequent 
on  the  varying  distance  of  the  sun.  The  principal  object 
of  the  tables  being  that  of  enabling  the  meteorologist  to 
ascertain  to  what  extent  the  result  of  his  observations  of 
solar  radiation  is  influenced  by  the  distance  of  the  sun,  it 
will  be  evident  that  some  zero  having  a  fixed  relation  to 
the  position  of  the  earth  in  its  orbit  should  be  adopted,  in 
order  to  render  comparisons  possible.  Accordingly,  the  ap- 
pended tables  have  reference  to  the  maximum  temperature 
produced  by  solar  radiation  when  the  earth  is  in  aphelion. 
The  utility  of  adopting  a  fixed  zero  will  be  seen  by  the  fol- 
lowing explanation :  Suppose  that  we  find  by  observation, 
during  bright  sunshine,  January  20,  that,  under  a  zenith  dis- 
tance of  68  deg.,  the  actinometer  indicates  54°.5  F.  Suppose, 
also,  that  our  records  of  solar  intensity  during  summer  show 
that,  June  15,  the  actinometer  indicated  49°.9  F.  at  equal  zenith 
distance — viz.,  68  deg.  Leaving  the  influence  of  solar  distance 
out  of  sight,  the  inference  would  be  that  the  diminished  inten- 
sity of  54.5  —  49.9  =  4°.6  F.,  observed  June  15,  was  owing  to 
the  presence  of  vapor  in  the  atmosphere.  Secchi  and  others, 
who  suppose  that  the  absorptive  power  of  the  atmosphere 
called  forth  by  vapor  prevents  the  full  development  of  solar 
radiation  at  all  times  during  summer,  would  not  hesitate  to 
ascribe  the  observed  diminution  of  radiant  intensity  to  that 


CHAP.  IV.     PEKIODIC  VARIATION  OF  HOLAU  RADIATION.  «1 

cause.  But  a  gluiu-e  at  our  table  at  once  ilisclascs  the  true 
cause  of  the  observed  difference  of  solar  intensity  under  equal 
zenith  distance  in  January  and  in  June.  Consulting-  the  table 
for  Jaiuiaiy,  and  running  the  eye  down  the  column  headed 
"  Increment,"  the  temperature  4°.6  will  be  found  opposite  the 
date  20tli  in  the  tirst  column.  Accordingly,  the  feebleness 
of  snlar  j-adiation  observed  in  the  middle  of  June,  instead  of 
being  caused  by  atmospheric  absorption,  is  solely  due  to  the 
increased  distance  of  the  earth  from  the  sun.  It  should  be 
observed  that  the  assumed  temperature  of  49°.9  F.,  at  a  zenith 
distance  of  GS  deg.  in  the  middle  of  June,  is  not  imagiuarj', 
having  frequently  been  observed  during  my  investigations  of 
solar  energy.  Again,  temperatures  exceeding  54°  F.  have  been 
observed  during  mid-winter  at  a  zenith  distance  of  68  deg. 

It  will  be  proper  to  remind  meteorologists  accustomed  to 
observe  the  intensity  of  solar  radiation,  hence  familiar  with 
the  extraordinaiy  discrepancy  of  observations  made  with  ordi- 
nary "  solar  radiation  thermometers,"  that  the  invariably  con- 
sistent indications,  and  the  freedom  from  conHicting  results, 
in  my  actinometric  observations  of  solar  energy,  are  chiefly 
due  to  the  fact  that  the  bulb  of  the  recording  thermometer 
is  enclosed  within  an  exhausted  vessel,  maintained  at  a  con- 
stant temperature  of  60°  F.  during  obser\'a(ions.  Hence,  ^\•he- 
ther  the  investigation  be  conducted  in  calms  or  high  winds, 
or  whether  the  thermometer  marks  100  in  the  shade  or  the 
temperature  of  the  air  be  below  zero,  no  material  error  is 
possible.  This  fact  merits  special  consideration  on  the  part 
of  those  who  have  questioned  the  possibility  of  determining 


82  BADIANT  MEAT.  chap.  iv. 

practically  to  \\'liat  degree  tlie  temperature  produced  by  solar 
radiation  is  increased  when  the  earth  is  in  perihelion.  And 
those  who  have  adopted  Herschel's  conclusion,  that  "  23°  Fah- 
renheit is  the  least  variation  of  temperature  which  can  reason- 
ably be  attributed  to  the  actual  variation  of  the  sun's  distance," 
will  do  well  to  contrast  the  reasoning  of  the  great  astronomer 
with  the  reasoning  which  assigns  5°  Fahrenheit  as  the  utmost 
increment  of  solar  intensity  in  the  southern  hemisphere,  con- 
sequent on  the  proximity  of  the  luminary  during  our  mid- 
winter. 

Regarding  the  construction  of  the  appended  tables  of  solar 
intensity,  the  following  explanation  and  recapitulation  will 
suffice  :  Having  determined  the  maximum  solar  intensity  when 
the  earth  is  in  aphelion,  in  accordance  with  the  data  furnished 
in  Chap.  III.,  the  maximum  intensity  in  perihelion  was  deter- 
mined by  computation  in  the  manner  already  pointed  out. 
The  result,  as  we  have  seen,  has  been  fully  corroborated  by 
actinometric  observation.  The  maximum  increment  of  tempe- 
rature produced  by  solar  radiation  when  the  earth  is  in  peri- 
helion having  been  fixed  at  4°.66  F.,  the  increment  of  tem- 
perature for  each  day  throughout  the  year  was  determined 
by  inverting  the  ratio  of  the  square  of  the  sun's  distance  from 
day  to  day. 

We  have  already  pointed  out  that  investigations  of  solar 
intensity  which  do  not  take  cognizance  of  the  influence  of  the 
sun's  distance  are  of  no  value.  Obviously,  the  difference  of 
temperature  produced  by  solar  radiation  furnishes  an  infal- 
lible index  of  atmospheric  absorption,  provided  we  make  due 


CHAP.  IV.     PERIODIC  VAIUATIOX  OF  tiOLAIi  RADIATION.  83 

allowance  for  the  sun's  zenith  distance  and  the  position  of  the 
earth  in  its  orbit  at  the  time  of  making  our  observation.  But, 
unless  suoli  allowance  be  made,  the  inference  we  draw  from  the 
indicated  temperatures  will  prove  wholly  erroneous. 

Respecting  the  mode  of  applying  the  tables,  it  will  be 
evident,  on  reflection,  that,  if  we  desire  to  ascertain  whether 
vajiors  are  present  in  the  atmosphere,  the  temperature  con- 
tained in  the  column  headed  "  Increment,"  for  the  day  on 
which  the  observation  is  made,  should  be  deducted  from 
the  temperature  indicated  by  the  actinometer.  Suppose,  for 
instance,  that  the  indicated  solar  intensity,  Aug.  26,  is  58°  F. 
at  a  zenith  distance  of  40  deg.  Deducting  from  58'  the  incre- 
ment of  temperature  entered  in  the  table  for  Aug.  26 — viz., 
0''.96 — consequent  on  the  diminished  distance  fi-om  the  sun, 
we  obtain  58  —  0.96  =  57^.04.  Now,  if  we  consult  the  table 
of  temperatures  for  given  zenith  distance  (see  page  62,  Chap, 
in.),  it  will  be  found  that  the  maximum  solar  temperature 
for  a  zenith  distance  of  40  deg.  should  be  61°.67.  Our  obser- 
vation of  Aug.  26,  therefore,  shows  that  the  vapors  contained 
in  the  atmosphere  have  absorbed  61.67  —  57.04  =  4°.63  of 
the  sun's  radiant  heat.  The  advantage  of  this  positive  mode 
of  ascertaining  the  absorptive  power — i.e.,  the  presence  of  vajtor 
in  the  atmosphere — meteorologists  cannot  fail  to  appreciate. 

The  close  agreement  between  the  computed  and  observed 
increment  of  the  temperature  produced  by  solar  radiation  when 
the  earth  is  in  perihelion,  before  adverted  to,  calls  for  special 
notice  in  this  place,  since  it  proves  the  correctness  of  the  acti- 
nometric  observations  recorded  in  Chap.  III.,  on  which  our 


8-i  BABIANT  HEAT.  chap.  iv. 

determination  of  the  varying  intensity  of  the  sun's  radiant 
heat  is  based.  It  will  be  evident  that,  if  our  determination 
of  maximum  solar  intensity  when  the  earth  is  in  aphelion 
(based  solely  on  our  observations)  were  incorrect,  the  infal- 
lible test  of  applying  the  law  of  inverse  squares  would  at 
once  expose  the  error.  Now,  this  test  has  been  applied  ;  we 
have  inverted  the  squares  of  the  relative  aphelion  and  peri- 
helion distance  of  the  earth,  and  we  find  that  in  the  latter 
position  an  increment  of  4°.  6  6  F.  results  from  the  proximity 
of  the  sun.  Our  ohservations  show  an  increment  of  4°.41  dif- 
ference =  0°,25  Fahrenheit. 


cuAP.  IV.    rEnioinc  vaiuatiox  of  solai;  hadiatios. 


T. 

IBLE   SHOWING    THE    MAXIMUM    INTENSITY 

OF  Solar  Radiation 

ON 

THE  Ecliptic. 

1 

JAyUARY. 

FEBRUARY. 

Maximum. 

Increment. 

Maximum. 

Increment. 

•  Fuh. 

°  Ctnt. 

'Fah. 

•  Cmt. 

i      •  Fah. 

'Ctnt. 

•Fah. 

'Cmt 

1 

71.94 

39.97 

4.66 

2.59 

71.59 

39.77 

4.31 

2.39 

2 

71.94 

39.97 

4.60 

2.59 

71.57 

39.76 

4.29 

2.38 

3 

71.94 

39.97 

4.66 

2.59 

71.54 

39.74 

4.26 

2.36 

4 

71.93 

39.97 

4.65 

2.59 

71.52 

39.73 

4.24 

2.35 

5 

71.93 

39.97 

4.65 

2.59 

71.50 

39.72 

4.22 

2.34 

6 

71.92 

39.96 

4.64 

2.58 

71.47 

39.71 

4.19 

2.33 

7 

71.92 

39.96 

4.64 

2.58 

71.45 

39.69 

4.17 

2.31 

8 

71.91 

39.95 

4.63 

2.57 

71.42 

39.68 

4.14 

2.30 

9 

71.91 

39.95 

4.63 

2.57 

71.40 

39.67 

4.12 

2.29 

10 

71.90 

39.94 

4.62 

2.56 

71.38 

39.65 

4.10 

2.27 

11 

71.90 

39.94 

4.62 

2.56 

71.35 

39.64 

4.07 

2.26 

12 

71.89 

39.93 

4.61 

2.55 

71.32 

39.62 

4.04 

2.24 

13 

71.88 

39.93 

4.60 

2.55 

71.29 

39.60 

4.01 

2.22 

14 

71.87 

39.92 

4.59 

2.54 

71.27 

39.59 

3.99 

2.21 

15 

71.86 

39.92 

4.58 

2.54 

71.24 

39.58 

3.96 

2.20 

16 

71.85 

39.91 

4.57 

2.53 

71.20 

39.56 

3.92 

2.18 

17 

71.84 

39.91 

4.56 

2.53 

71.17 

39.54 

3.89 

2.16 

IS 

71.82 

39.90 

4.54 

2.52 

71.14 

39.52 

3.86 

2.14 

19 

71.81 

39.90 

4.53 

2.52 

71.11 

39.50 

3.83 

2.12 

20 

71.80 

39.89 

4.52 

2.51 

71.08 

39.49 

3.80 

2.11 

21 

71.78 

39.88 

4.50 

2.50 

71.05 

39.47 

3.77 

2.09 

22 

71.77 

39.87 

4.49 

2.49 

71.02 

39.45 

3.74 

2.07 

23 

71.76 

39.87 

4.48 

2.48 

70.98 

39.43 

3.70 

2.05 

24 

71.74 

39.86 

4.46 

2.47 

70.95 

39.42 

3.67 

2.04 

25 

71.72 

39.84 

4.44 

2.46 

70.02 

39.40 

3.64 

2.02 

2G 

71.70 

39.83 

4.42 

2.45 

70.88 

39.38 

3.60 

2.00 

27 

71.68 

39.82 

4.40 

2.44 

70.85 

39.36 

3.57 

1.98 

28 

71.67 

39.81 

4.39 

2.43 

70.82 

39.34 

3.  .54 

1.90 

20 

71.65 

39.80 

4.37 

2.42 

3(J 

71.63 

39.79 

4.35 

2.41 

31 

71. Gl 

39.78 

4.33 

•J. -10 

8G 


EADIANT  UEAT. 


Table  siiowinr  the  Maximum:  Intensity 

OF  Solar  Radiation 

ON 

THE  Ecliptic. 

MARCH. 

APRIL. 

Maximum. 

Increment. 

Maximum. 

Increment. 

°Fah. 

'  Cent. 

°  Fah. 

'  Cent. 

'Fah. 

'  Cent. 

°  Fah. 

'  Cent. 

1 

70.79 

39.33 

3.51 

1.95 

69.60 

38.67 

2.32 

1.29 

2 

70.75 

39.31 

3.47 

1.93 

69.56 

38.64 

2.38 

1.26 

3 

70.72 

39.29 

3.44 

1.91 

69.52 

38.62 

2.24 

1.24 

4 

70.08 

39.27 

3.40 

1.89 

69.48 

38.60 

2.20 

1.22 

5 

70.65 

39.25 

3.37 

1.87 

69.44 

38.58 

2.16 

1.20 

6 

70.61 

39.23 

3.33 

1.85 

69.40 

38.56 

2.12 

1.18 

7 

70.58 

39.21 

3.30 

1.83 

69.36 

38.53 

2.08 

1.15 

8 

70.54 

39.19 

3.26 

1.81 

69.32 

38.51 

2.04 

1.13 

9 

70.50 

39.17 

3.22 

1.79 

69.28 

38.49 

2.00 

1.11 

10 

70.46 

39.14 

3.18 

1.76 

69.24 

38.47 

1.96 

1.09 

11 

70.42 

39.12 

3.14 

1.74 

69.20 

38.44 

1.92 

1.06 

12 

70.38 

39.10 

3.10 

1.72 

69.16 

38.42 

1.88 

1.04 

13 

70.35 

39.08 

3.07 

1.70 

69.13 

38.40 

1.85 

1.02 

14 

70.31 

39.06 

3.03 

1.68 

69.09 

38.38 

1.81 

1.00 

15 

70.27 

39.04 

2.99 

1.66 

69.05 

38.36 

1.77 

0.98 

16 

70.23 

39.02 

2.95 

1.64 

69.01 

38.34 

1.73 

0.96 

17 

70.19 

38.99 

2.91 

1.61 

68.97 

38.32 

1.69 

0.94 

18 

70.15 

38.97 

2.87 

1.59 

68.93 

38.29 

1.65 

0.91 

19 

70.12 

38.95 

2.84 

1.57 

68.89 

38.27 

1.61 

0.89 

20 

70.08 

38.93 

2.80 

1.55 

68.85 

38.25 

1.57 

0.87 

21 

70.04 

38.91 

2.76 

1.53 

68.81 

38.23 

1.53 

0.85 

22 

70.00 

38.89 

2.72 

1.51 

68.78 

38.21 

1.50 

0.83 

23 

69.96 

38.87 

2.68 

1.49 

68.74 

38.19 

1.46 

0.81 

24 

69.92 

38.84 

2.64 

1.46 

68.70 

38.17 

1.42 

0.79 

25 

69.88 

38.82 

2.60 

1.44 

68.66 

38.14 

1.38 

0.76 

26 

69.84 

38.80 

2.56 

1.42 

68.63 

38.12 

1.35 

0.74 

27 

69.80 

38.78 

2.52 

1.40 

68.59 

38.10 

1.31 

0.72 

28 

69.76 

38.75 

2.48 

1.37 

68.55 

38.08 

1.27 

0.70 

29 

69.72 

38.73 

2.44 

1.35 

68.52 

38.06 

1.24 

0.68 

80 

69.68 

38.71 

2.40 

1.33 

68.48 

38.04 

1.20 

0.66 

31 

69.64 

38.60 

2.36 

1.31 

cuAP.  IV.   rEiiioDia  VAitiATJoy  of  solak  riAniAiwy. 


87 


Table  siiowin-g  tiik  Maximum  Isteksity 

OF   SOLAE 

Kadiatiox     1 

ox 

rnrc  Ecliptic. 

"a 

MAY. 

jm'E. 

Maximum. 

Increment. 

Maximum. 

Increment. 

•Fall. 

•  Ctnt. 

'Fah. 

•Ctnt. 

•Fah. 

•  Cent. 

•Fak. 

•Cent. 

1 

68.45 

38.03 

1.17 

0.65 

67.58 

37.54 

0.30 

0.16 

2 

68.41 

38.01 

1.13 

0.63 

67.56 

37.53 

0.28 

0.15 

3 

68.38 

37.99 

1.10 

0.61 

67.54 

37.52 

0.26 

0.14 

4 

68.35 

37.97 

1.07 

0.59 

67.52 

37.51 

0.24 

0.13 

5 

68.32 

37.95 

1.04 

0.57 

67.51 

37.50 

0.23 

0.12 

6 

68.28 

37.93 

1.00 

0.55 

67.49 

37.49 

0.21 

0.11 

7 

68.25 

37.92 

0.97 

0.54 

67.47 

37.48 

0.19 

0.10 

8 

68.22 

37.90 

0.94 

0.52 

67.46 

37. -18 

0.18 

0.10 

9 

68.19 

37.88 

0.91 

0.50 

67.44 

37.47 

0.10 

0.09 

10 

68.16 

37.87 

0.88 

0.49 

67.43 

37.40 

0.15 

0.08 

11 

68.13 

37.85 

0.85 

0.47 

67.42 

37.45 

0.14 

0.07 

12 

68.10 

37.83 

0.82 

0.45 

67.40 

37.44 

0.12 

0.06 

13 

68.06 

37.81 

0.78 

0.43 

67.39 

37.44 

0.11 

0.06 

14 

68.03 

37.79 

0.75 

0.41 

67.38 

37.43 

0.10 

0.05 

15 

68.00 

37.78 

0.72 

0.40 

67.37 

37.43 

0.09 

0.05 

16 

67.97 

37.76 

0.69 

0.38 

67.36 

37.42 

0.08 

0.04 

17 

67.94 

37.74 

0.60 

0.36 

67.35 

37.42 

0.07 

0.04 

18 

67.91 

37.73 

0.63 

0.35 

07.34 

37.41 

0.06 

0.03 

19 

67.89 

37.72 

0.61 

0.34 

67.33 

37.40 

0.05 

0.02 

20 

67.86 

37.70 

0..58 

0.32 

67.32 

37.40 

0.04 

0.02 

21 

67.84 

37.09 

0.56 

0.31 

67.32 

37.40 

0.04 

0.02 

22 

67.81 

37.67 

0.53 

0.29 

67.31 

37.39 

0.03 

0.01 

23 

67.79 

37.66 

0.51 

0.28 

67.30 

37.39 

0.02 

0.01 

24 

67.77 

37.65 

0.49 

0.27 

67.30 

37.39 

0.02 

0.01 

25 

67.75 

37.64 

0.47 

0.26 

67.29 

37.38 

0.01 

0.00 

26 

67.72 

37.62 

0.44 

0.24 

67.29 

37.38 

0.01 

0.00 

27 

67.70 

37.61 

0.42 

0.23 

67.28 

37.38 

0.00 

0.00 

28 

67.67 

37.59 

0.39 

0.21 

67.28 

37.38 

0.00 

0.00 

29 

67.65 

37.58 

0.37 

0.20 

67.28 

37.38 

0.00 

0.00 

30 

67.63 

37.57 

0.35 

0.19 

67.28 

37.38 

0.00 

0.00 

31 

67.60 

37.  .55 

0.32 

0.17 

88 


RADIANT  HEAT. 


T. 

BLE    SHOWING   TUB    MaXIMUSI    INTENSITY 

Of    80LA1 

.  Radiation 

ON 

THE  Ecliptic. 

1 

JULY. 

AUGUST. 

Maximum. 

Increment. 

Maximum. 

Increment. 

'  FaJi. 

°  Cent. 

°  Fah. 

°  Cent. 

°  Fah. 

°  Cent. 

•  Fah. 

°  Cent. 

1 

67.28 

37.88 

0.00 

0.00 

67.58 

87.54 

0.30 

0.16 

2 

67.28 

37.88 

0.00 

0.00 

67.60 

87.55 

0.32 

0.17 

3 

07.28 

37.38 

0.00 

0.00 

67.63 

87.57 

0.35 

0.19 

■1 

67.28 

87.38 

0.00 

0.00 

67.65 

37.58 

0.87 

0.20 

5 

67.28 

87.38 

0.00 

0.00 

67.67 

37.59 

0.89 

0.21 

6 

67.28 

87.38 

0.00 

0.00 

67.70 

37.61 

0.42 

0.23 

7 

67.29 

87.38 

0.01 

0.00 

67.72 

37.62 

0.44 

0.24 

8 

67.29 

87.38 

0.01 

0.00 

67.75 

37.04 

0.47 

0.26 

9 

67.30 

37.39 

0.02 

0.01 

67.77 

37.65 

0.49 

0.27 

10 

67.30 

87.39 

0.02 

0.01 

67.79 

37.66 

0.51 

0.28 

11 

67.31 

87.89 

0.03 

0.01 

67.81 

37.67 

0.53 

0.29 

12 

67.32 

37.40 

0.04 

0.02 

67.84 

87.69 

0.56 

0.31 

13 

67.32 

37.40 

0.04 

0.02 

67.86 

37.70 

0.58 

0.32 

14 

67.33 

87.41 

0.05 

0.08 

67.89 

37.72 

0.61 

0.34 

15 

67.34 

37.41 

0.06 

0.08 

67.91 

37.73 

0.63 

0.35 

16 

67.35 

37.42 

0.07 

0.04 

67.94 

37.74 

0.66 

0.36 

17 

67.36 

37.42 

0.08 

0.04 

67.97 

37.76 

0.69 

0.88 

18 

67.37 

37.48 

0.09 

0.05 

68.00 

37.78 

0.72 

0.40 

19 

67.38 

37.43 

0.10 

0.05 

68.03 

87.79 

0.75 

0.41 

20 

67.39 

37.44 

0.11 

0.06 

68.06 

37.81 

0.78 

0.43 

21 

67.40 

37.44 

0.12 

0.06 

68.10 

87.88 

0.82 

0.45 

22 

67.42 

37.45 

0.14 

0.07 

68.13 

37.85 

0.85 

0.47 

23 

67.43 

37.46 

0.15 

0.08 

68.16 

87.87 

0.88 

0.49 

24 

67.44 

37.47 

0.16 

0.09 

68.19 

37.88 

0.91 

0.50 

25 

67.46 

37.48 

0.18 

0.10 

68.22 

87.90 

0.94 

0.52 

26 

67.47 

37.48 

0.19 

0.10 

68.25 

37.92 

0.97 

0.54 

27 

67.49 

87.49 

0.21 

0.11 

68.28 

87.93 

1.00 

0.55 

28 

67.51 

37.50 

0.28 

0.12 

68.32 

37.95 

1.04 

0.57 

29 

67.52 

37.51 

0.24 

0.13 

68.35 

37.97 

1.07 

0.59 

30 

67.54 

87.52 

0.26 

0.14 

68.38 

87.99 

1.10 

0.61 

31 

67.56 

37.58 

0.28 

0.15 

68.41 

38.01 

1.13 

0.63 

IV.    PERIODIC  rAlilArWN  OF  SOLAI!  umumios. 


so 


Table  showing  the 

Maximum  I.ntensity  of  Solar 

Radiation- 

ON  the  Ecliptic. 

i 

1 
SEPTEMBER.                 1 

OCTOBER. 

Maximum. 

Increment. 

Maximum. 

Increment. 

'rah. 

'Cmi. 

'Fali.    1 

•  On*,      j 

'Fah. 

'  Cmt. 

•Fah. 

•0«i<. 

1 

68.45 

38.03 

1.17 

0.65 

69.«0 

38.67 

2.32 

1.29 

2 

68.48 

38.04 

1.20 

0.66 

69.64 

38.69 

2.36 

1.31 

3 

68.52 

38.06 

1.24 

0.68 

69.68 

38.71 

2.40 

1.33 

4 

68.55 

38.08 

1.27 

0.70 

69.72 

38.73 

2.44 

1.35 

5 

68.59 

38.10 

1.31 

0.72 

69.76 

38.75 

2.48 

1.37 

6 

68.63 

38.12 

1.35 

0.74 

69.80 

38.78 

2.52 

1.40 

7 

68.66 

38.14 

1.38 

0.76 

69.84 

38.80 

2.56 

1.42 

8 

68.70 

38.17 

1.42 

0.79 

69.88 

38.82 

2.60 

1.44 

9 

68.74 

38.19 

1.46 

0.81 

69.92 

38.84 

2.64 

1.40 

10 

68.78 

38.21 

1.50 

0.83 

69.96 

38.87 

2.68 

1.49 

11 

68.81 

38.23 

1.53 

0.85 

70.00 

38.89 

2.72 

1.51 

12 

68.85 

38.25 

1.57 

0.87 

70.04 

38.91 

2.76 

1.53 

13 

68.89 

38.27 

1.61 

0.89 

70.08 

38.93 

2.80 

1.55 

14 

68.93 

38.29 

1.65 

0.91 

70.12 

38.95 

2.84 

1.57 

15 

68.97 

38.32 

1.69 

0.94 

70.15 

38.97 

2.87 

1.59 

16 

69.01 

38.34 

1.73 

0.96 

70.19 

38.99 

2.91 

1.61 

17 

69.05 

38.30 

1.77 

0.98 

70.23 

39.02 

2.95 

1.64 

18 

69.09 

38.38 

1.81 

1.00 

70.27 

39.04 

2.99 

1.66 

19 

69.13 

38.40 

1.85 

1.02 

70.31 

39.06 

3.03 

1.68 

20 

69.16 

38.42 

1.88 

1.04 

70.35 

39.08 

3.07 

1.70 

21 

69.20 

38.44 

1.92 

1.06 

70.38 

39.10 

3.10 

1.72 

22 

69.24 

38.47 

1.96 

1.09 

70.42 

39.12 

3.14 

1.74 

23 

69.28 

38.49 

2.00 

1.11 

70.46 

39.14 

3.18 

1.70 

24 

69.32 

38.51 

2.04 

1.13 

70.50 

39.17 

3.22 

1.79 

25 

69.36 

38.53 

2.08 

1.15 

70.54 

39.19 

3.26 

1.81 

26 

69.40 

38.56 

2.12 

1.18 

70.58 

39.21 

3.30 

1.83 

27 

69.44 

38.58 

2.16 

1.20 

70.61 

39.23 

3.33 

1.85 

28 

69.48 

38.60 

2.20 

1.22 

70.65 

39.25 

3.37 

1.87 

29 

69.52 

38.62 

2.24 

1.24 

,    70.08 

39.27 

3.40 

1.89 

30 

69.56 

38.64 

2.28 

1.26 

70.72 

39.29 

3.44 

1.91 

31 

... 

... 

'    70.75 

39.31 

3.47 

1.93 

90 


lUBIAXT  HEAT. 


Table  showikg  the  Maximum  Intensity 

OF  Solar  Eadiation 

ox 

THE  Ecliptic. 

si 

A^ormiBEB. 

DECEMBER. 

Maximum. 

Increment. 

Maxiiniim. 

Increment. 

'Fah. 

°  Cent. 

°  Fah. 

•  Cent. 

°  Fah. 

°  Cent. 

'Fah. 

"  Cent. 

1 

70.79 

39.33 

3.51 

1.95 

71.63 

39.79 

4.85 

2.41 

2 

70.82 

39.34 

3.54 

1.96 

71.65 

39.80 

4.37 

2.42 

3 

70.85 

39.36 

3.57 

1.98 

71.67 

39.81 

4.39 

2.43 

4 

70.88 

39.38 

3.60 

2.00 

71.68 

39.82 

4.40 

2.44 

i) 

70.92 

39.40 

3.64 

2.02 

71.70 

39.83 

4.42 

2.45 

6 

70.95 

39.42 

3.67 

2.04 

71.72 

39.84 

4.44 

2.46 

7 

70.98 

39.43 

3.70 

2.05 

71.74 

39.86 

4.46 

2.47 

8 

71.02 

39.45 

3.74 

2.07 

71.76 

39.87 

4.48 

2.48 

9 

71.05 

39.47 

3.77 

2.09 

71.77 

39.87 

4.49 

2.49 

10 

71.08 

39.49 

3.80 

2.11 

71.78 

39.88 

4.50 

2.50 

11 

71.11 

39.50 

3.83 

2.12 

71.80 

39.89 

4.52 

2.51 

12 

71.14 

39.52 

3.86 

2.14 

71.81 

39.90 

4.68 

2.52 

13 

71.17 

39.54 

3.89 

2.16 

71.82 

89.90 

4.54 

2.52 

14 

71.20 

39.56 

3.92 

2.18 

71.84 

89.91 

4.56 

2.53 

15 

71.24 

39.58 

3.96 

2.20 

71.85 

39.91 

4.57 

2.53 

10 

71.27 

39.59 

3.99 

2.21 

71.86 

89.92 

4.58 

2.54 

17 

71.29 

39.60 

4.01 

2.22 

71.87 

39.92 

4.59 

2.54 

18 

71.32 

39.62 

4.04 

2.24 

71.88 

39.93 

4.60 

2.55 

19 

71.35 

39.64 

4.07 

2.26 

71.89 

39.93 

4.61 

2.55 

20 

71.38 

39.65 

4.10 

2.27 

71.90 

39.94 

4.62 

2.56 

21 

71.40 

39.67 

4.12 

2.29 

71.90 

39.94 

4.62 

2.56 

22 

71.42 

39.68 

4.14 

2.30 

71.91 

39.95 

4.63 

2.57 

23 

71.45 

39.69 

4.17 

2.31 

71.91 

39.95 

4.63 

2.57 

24 

71.47 

39.71 

4.19 

2.33 

71.92 

39.96 

4.64 

2.58 

2o 

71.50 

39.72 

4.22 

2.34 

71.92 

39.96 

4.64 

2.58 

20 

71.52 

39.73 

4.24 

2.35 

71.93 

39.97 

4.65 

2.59 

27 

71.54 

39.74 

4.26 

2.36 

71.93 

39.97 

4.65 

2.59 

28 

71.57 

39.76 

4.29 

2.38 

71.94 

39.97 

4.66 

2.59 

29 

71.59 

39.77 

4.31 

2.39 

71.94 

39.97 

4.66 

2.59 

30 

71.01 

39.78 

4.83 

2.40 

71.94 

39.97 

4.66 

2.59 

31 

71.94 

39.97 

4.00 

2.59 

CHAPTER  V. 

MECHANICAL  ENEKGY  OF  SOLAR  RADIATION. 


The  mechanical  energy  developed  by  solar  radiation  cannot 
be  accurately  determined  unless  we  possess  means  of  ascertain- 
ing (1)  the  energy  actually  called  forth  by  the  sun's  radiant 
heat  at  the  surface  of  the  earth,  and  (2)  the  energy  lost  during 
the  passage  of  the  rays  through  our  atmosphere.  The  illus- 
tration shown  on  Plate  10  represents  a  solar  calorimeter, 
an  instrument  constnicted  for  measuring  the  energy  actually 
developed  near  the  earth's  surface.  An  instrument  for  mea- 
suiing  the  amount  of  radiant  heat  absorbed  by  the  atmosphere, 
the  actinometer,  has  been  fully  described  in  Chapter  III.  Evi- 
dently, if  we  possess  reliable  means  of  ascertaining  the  heat 
developed  on  a  given  area  at  the  surface  of  the  earth,  and 
that  lost  by  atmospheric  absoi-ption,  we  can  state  positively 
what  amount  of  dynamic  energy  is  developed  on  a  given  area 
by  solar  radiation  at  the  boundary  of  the  terrestrial  atmo- 
sphere. And  since  we  know  the  tnie  relation  between  the 
semi-diameter  of  the  sun  and  the  distance  from  the  sun's  centre 


92  L'AliIAXT  HEAT.  chap.  V. 

to  the  earth,  we  can  calciUate  the  exact  degree  of  dispersion 
of  the  solar  rays  on  reaching  the  atmospheric  boundary.  Ac- 
cordingly, we  possess  all  the  elements  necessary  to  compute 
the  amount  of  mechanical  energy  transmitted  by  radiation 
from  a  given  area  of  the  surface  of  the  sun.  Now,  it  will 
be  found,  on  referring  to  Chap.  VI.,  that  the  sun  emits  heat 
of  equal  energy  in  all  directions ;  hence  we  are  enabled  to 
estimate  the  total  amount  of  mechanical  power  developed  and 
transmitted  by  the  sun  as  a  motor. 

Sir  John  Herschel  and  M.  Pouillet  conceived  the  idea, 
nearly  at  the  same  time,  of  measuring  the  energy  of  solar 
radiation  by  exposing  a  given  quantity  of  water,  presenting 
a  given  area,  to  the  sun's  rays.  Having  ascertained  the  ele- 
vation of  temperature  of  the  water  acquired  in  a  given  time, 
and  added  the  energy  suj)posed  to  be  lost  by  atmospheric 
absorption,  together  with  the  loss  consequent  on  the  disper- 
sion of  the  rays,  they  computed  the  total  dynamic  energy 
developed  by  the  sun.  Herschel  employed  a  small,  stationary, 
open  vessel,  which  he  termed  an  actinometer ;  while  Pouillet 
resorted  to  a  close,  movable  vessel,  the  well-knowai  "  pyrhe- 
liometre."  The  simple  instrument  devised  by  the  great  Eng- 
lish astronomer,  althoiigh  very  defective  and  incapable  of 
furnishing  exact  data,  demands  particular  notice,  since  it 
was  employed  in  the  ftrst  investigation  of  a  practical  nature 
intended  to  solve  the  important  problem  of  solar  energy. 
The  result  of  the  investigation  of  Herschel,  it  will  be  remem- 
bered, startled  the  Avorld  by  the  inconceivable  magnitude  of 
solar  energy  which  it  disclosed.     The  actinometer,  agreeably 


CHAP.  V.     MECHANICAL  ENERGY  OF  SOLAR  RADIATION.  9o 

to  the  following  lucid  statement,  furnished  by  the  distin- 
guished designer  himself,  consisted  of  "  a  light  cylindrical 
vessel  of  tinned  iron,  open  at  the  top,  3f  inches  in  diameter 
and  2.4  inches  in  depth,  weighing  1,069  grains,  nearly  filled 
with  water  moderately  darkened  by  a  slight  admixture  of 
ink.  This  vessel  was  placed  on  a  light  wooden  support, 
covered  with  cotton  cloth,  and  touching  it  only  in  a  narrow 
ring  (to  avoid  the  communication  of  heat  by  conduction),  in 
the  interior  of  an  iron  cylinder  of  much  larger  diameter,  to 
protect  it  from  wind  and  external  radiation,  the  upper  part 
of  which  was  covered  by  an  iron  plate  ^vell  protected  from 
sunshine  by  several  separate  diaphragms  of  paper  laid  lightly 
one  over  the  other  thereon.  This  plate  had  a  circular  aper- 
tui'e  somcAvhat  wider  than  that  of  the  tin  cylinder,  and  ver- 
tically over  it,  centre  corresponding  to  centre.  The  mouth 
of  the  tin  cylinder  was  covered  with  a  circle  of  stiff  paper, 
having  an  aperture  exactly  circular  and  concentric  with  the 
cylinder,  so  as  to  admit  a  vertical  or  nearly  vertical  sunbeam 
somewhat  less  in  section  than  the  vessel,  and  loholly  incident 
on  the  surface  of  the  contained  liquid.  This  cover  also  pro- 
jected over  the  exterior  of  the  cylinder  on  all  sides,  so  as 
to  prevent  any  ray  from  striking  ou  its  outside,  even  when 
the  uj^per  iron  plate  was  removed  from  the  exterior  vessel. 
Lastly,  to  cut  off  effectually  all  lateral  radiation  from  the 
region  of  sky  near  the  sun,  a  paper  diaphragm  but  very  little 
more  in  aperture  than  the  mouth  ol'  the  tin  cylinder  was  laid 
concentrically  on  the  upper  iron  plate  and  its  diaphragms. 
Plunged  into  the  liquid,  and  resting  on  the  bottom  when  not 


94  BABIANT  HEAT.  chap.  V. 

in  use,  was  a  circular  plate  of  mica  '6\  inches  in  diameter, 
attaclied  to  a  light  rod  of  reed  0.1  inch  in  diameter,  for  the 
purpose  of  completely  stirring  and  mixing  the  strata  of  the 
liquid  by  one  or  two  up  and  down  movements.  When  thus 
prepared,  the  whole  apparatus  was  placed  in  the  sunshine 
at  noon,  or  somewhat  before,  and  so  adjusted  that,  on  the 
admission  of  sunlight,  a  narrow  ring  of  light  surrounded  con- 
centrically the  aperture  in  the  diaphragm  of  the  tin  cylinder 
beneath,  which  was  carefully  watched  during  the  progress 
of  the  experiment,  and  kept  unaltered.  These  arrangements 
being  made,  the  sun  was  shaded  off,  the  temperature  of  the 
lit[uid  (after  stirring  by  the  mica  plate)  taken  by  an  exceed- 
ingly delicate  and  sensitive  thermometer  by  Crichton,  and 
again  after  a  certain  noted  number  of  minutes.  The  shade 
being  then  removed,  the  sun  was  allowed  to  shine  into  the 
aperture  on  the  liquid  for  ten  minutes.  During  this  exjio- 
sure,  the  liquid  was  three  times  stirred  by  the  mica  plate, 
allowing  five  seconds  for  each  stirring,  and  shading  the  aper- 
ture during  that  operation  (which,  of  course,  was  not  counted 
as  part  of  the  ten  minutes'  exposure).  The  temperature  was 
now  again  taken,  and,  after  remaining  shaded  again  a  certain 
noted  number  of  minutes,  finally  once  more.  The  mean  of 
the  minutely  change  of  temperature,  deduced  from  the  shade 
observations,  being  obtained,  was  applied  as  a  correction  (in 
all  cases  a  very  small  one)  to  the  minutely  elevation  of  tem- 
perature in  the  sun  exposure ;  and  thus  the  true  effect  of  the 
Sim  was  concluded." 

The  "  pyrheliometre  "  having  been  described  in  nearly  all 


CHAP.  V.       MECHANICAL  EXEROT  OF  SOLAR  RADIATION.  95 

recent  works  on  solar  energy,  and  accurately  delineated  in 
Pouillet's  ":^lement8  de  Physique"  (Tome  II.,  Paris,  1856), 
it  will  only  be  necessaiy  to  remind  the  reader  that  the  vessel 
exposed  to  the  sun,  composed  of  polished  silver,  contains  100 
grammes  of  water.  The  diameter  is  1  decimetre  and  the  depth 
15  millimetres,  the  top  exposed  to  the  sun's  rays  being  coated 
with  lamp-black.  The  radical  defect  of  Pouillet's  instrument 
is  that  it  cannot  be  used  during  winter  when  the  tlierniometer 
is  below  the  freezing  point,  as  warm  water  would  have  to  be 
used,  in  which  case  the  loss  of  heat  by  radiation  and  convec- 
tion would  be  so  great  as  to  render  the  task  futile  of  accu- 
rately measuring  the  force  of  solar  radiation.  This  defect  of 
Pouillet's  method  is  the  more  serious  as  the  heat  of  the  sun 
is  most  intense  during  the  winter  solstice  for  given  zenith 
distances,  on  account  of  the  diminished  distance  between  the 
sun  and  the  earth,  and  because  the  sky  is  generally  clearer 
on  a  cold  winter's  day  than  during  the  heat  of  summer  when 
the  air  is  charged  with  vapor. 

The  loss  of  heat  by  radiation,  in  the  pyrheliometre ;  the 
loss  of  heat  by  convection,  accelerated  by  currents  of  air ;  the 
absence  of  adequate  means  for  circulating  the  fluid  contained 
within  the  heater ;  the  rade  method  of  keeping  the  instrument 
pei-pendicular  to  the  sun  wiih  the  hand,  not  to  mention  tlu- 
disturbing  influence  of  respiration  and  the  radiation  from  the 
operator's  body,  are  self-evident  defects.  Nor  can  we  pass 
unnoticed  the  want  of  any  direct  means  of  ascertaining  the 
depth  of  the  atmosphere  through  which  the  radiant  heat 
passes  at  the  moment  of  measuring  its  energy.     I  need  scarcely 


96  BADIAXT  HEAT.  en  A  p.  v. 

point  out  that  computations  based  on  latitude,  date,  and  exact 
time  are  too  complex  and  tedious  for  investigations  in  which 
the  principal  element,  the  depth  of  the  atmosphere,  is  con- 
tinually changing. 

It  will  be  well  to  state  that  the  solar  calorimeter,  and 
all  my  instruments  constructed  for  investigating  the  mecha- 
nical properties  of  solar  heat,  are  attached  to  a  vibrating 
table  applied  within  a  revolving  observatory,  supported  on 
horizontal  journals  and  provided  with  a  declination  movement 
and  a  graduated  arc.  Consequently,  the  sun's  zenith  distance 
may  at  all  times  be  ascertained  by  mere  inspection,  a  very 
great  convenience  in  an  investigation  which  at  every  instant 
is  dependent  on  the  changing  depth  of  the  atmosphere  through 
\\hich  the  solar  rays  pass.  As  this  depth  bears  a  fixed  rela- 
tion to  the  sun's  zenith  distance,  it  may  of  course  be  accurately 
determined  by  noting  the  position  of  the  fixed  index  on  the 
graduated  arc ;  but,  as  already  pointed  out,  there  is  no  time 
during  investigations  of  this  kind  for  computations.  I  have, 
therefore,  constructed  a  graduated  scale  provided  with  a  mov- 
able radial  index,  which,  by  being  brought  to  the  division 
corresponding  with  the  observed  zenith  distance,  shows  the 
depth  of  atmosphere  (see  diagram  in  Chap.  III.,  Plate  9). 
It  is  proper  to  observe  that,  in  constructing  this  scale,  I  have 
assumed  the  earth  to  be  a  perfect  sphere  of  3,956  miles  radius. 
The  error  resulting  from  this  assumption  is,  however,  so  trifling 
that  the  described  graphic  method  of  ascertaining  the  dejith 
of  the  atmosphere  may,  without  appreciable  error,  be  employed 
for  all  latitudes.     The  solar  calorimeter  consists  of  a  double 


CHAP.  V.      MLCIIASIVAL  KyEnay  OF  no  LA  n  1;A1>IATUk\.  'J7 

vessel,  cyliudriciil  at  the  bottom  uikI  conical  tit  the  top,  an 
8-iii.  lens  being  inserted  at  the  wide  end  in  the  manner  shown 
by  the  illustration.  The  interior  is  lined  with  polished  silver, 
the  space  between  the  two  vessels  being  closed  at  the  toji  and 
l)ottom  Ijy  means  of  perforated  rings,  as  shown  in  the  trans- 
verse section.  The  object  of  these  perforations  is  that  of  dis- 
tributing equally  a  current  of  water  to  be  circulatc<l  thrcmgh 
the  s]>ace  between  the  vessels.  Nozzles  are  ajipliiMJ  at  the 
top  and  bottom  of  the  external  vessel,  of  suitable  form  to 
admit  of  small  flexible  pipes  being  attached.  A  stop-cock 
with  coupling-joint  is  applied  at  the  bottom,  comnmnicating 
witli  the  interior  chamber  of  the  calorimeter  and  connected 
with  an  air-pump,  for  exhausting  the  same.  A  cylindrical 
vessel,  ^\•ith  closed  ends,  composed  of  ])olislied  silver,  is  secured 
in  the  lower  part  of  the  interior  chamber,  and  provided  with 
a  conical  nozzle  at  the  top,  through  which  a  thermometer  is 
inserted  from  -without.  Within  the  lower  part  of  this  cylin- 
drical vessel  a  centrifugal  paddle-wheel  is  applied,  surrounded 
by  a  cylimhii'al  casing  divided  into  two  compartments  by  a 
circular  diaphragm.  The  lower  compartment  contains  four 
i-adial  wings,  or  paddles,  the  diaphragm  being  perforated  in 
the  centre.  The  said  paddle-wheel  revolves  on  a  vertical  axle, 
which  passes  through  a  stuffing-box  applied  at  the  bottom  of 
the  surrounding  vessels,  the  rotary  motion  being  imparted  by 
means  of  a  pulley  secured  to  the  lower  end  of  the  axle.  The 
operation  of  this  wheel,  designed  to  proipote  perfect  circula- 
tion of  the  fluid  witliin  the  cylindrical  vessel  when  charged, 
is   quite   peculiar.      It    will   be  readily    understood   that   the 


98  RADIANT  HEAT.  CHAP.  X. 

centrifugal  action  produced  by  the  rotation  of  tlie  paddles 
Avill  draw  in  water  downwards  through  the  central  perfora- 
tion of  the  diaphragm,  and  force  the  same  into  the  annular 
space  round  the  casing  of  the  wheel ;  thus  an  upward  current 
^vill  be  kept  \\])  through  this  annular  space  uniform  on  all 
sides.  The  circulating  water,  after  reaching  the  top  of  the 
heater,  will  then  retui-n,  first  entering  the  open  end  of  the 
casing  of  the  wheel,  and  ultimately  the  central  perforation 
of  the  diaphragm.  I  have  been  thus  particular  in  describing 
this  system  of  pi-omoting  uniform  cii'culation,  because  a  correct 
indication  of  the  mean  temj)erature  of  the  water  contained 
within  the  vessel  subjected  to  the  action  of  the  concentrated 
rays,  is  the  all-important  condition  on  which  depends  the 
accuracy  of  the  determination  of  the  number  of  thermal  units 
developed  by  the  radiant  heat.  It  only  remains  to  be  pointed 
out  that  the  lens,  which  is  so  proportioned  as  to  admit  a  sun- 
beam of  53.45  sq.  ins.  of  section,  is  j)laced  at  such  a  distance 
from  the  heatei'  that  when  the  concentrated  rays  reach  the 
upper  end  (coated  with  lamp-black)  they  are  confined  to  an 
area  of  3.35  sq.  ins.,  viz.,  -j^  of  the  sectional  area  of  the  pencil 
of  rays  which  enters  the  lens. 

It  will  be  obvious  that  the  concentration  of  the  radiant 
heat  on  an  area  of  only  one-sixteenth  of  that  of  the  section 
of  the  pencil  of  rays  admitted  to  the  instrument  removes 
a  very  difiicult  disturbing  element  from  the  investigation — 
namely,  the  great  amount  of  heat  radiated  by  the  blackened 
surface  of  the  heater,  which  in  the  pyrheliometre  is  16  times 
greater  for  a  given  amount  of  radiant  heat  than  in  the  solar 


Cll.vi'.  V.      MEVUASIVAL  ESKUGY  OF  SOLAR  It  AVIATION.  911 

caloiimt'ter.  But  this  is  not  all ;  while  the  extensive  black- 
ened sui-face  of  the  former  is  exposed  to  currents  of  air,  the 
disturbing  effect  of  wliicli  can  neither  be  controlled  nor  com- 
puted, error  arising  from  convection  is  wholly  removed  from 
the  latter,  because  the  reduced  blackened  surface  oi  the  vessel 
exposed  to  the  solar  rays  receives  the  concentrated  radiant  heat 
within  a  vacuum.  The  loss  of  heat  at  the  bottom  and  sides 
of  Pouil let's  instrument,  caused  liy  convection  and  currents  of 
air,  is  likewise  wholly  removed  in  the  solar  calorimeter  \)\ 
the  expedient  of  operating  within  a  vacuum.  It  ^vill  be  seen, 
therefore,  that  the  loss  from  these  causes  has  been  wholly  obvi- 
ated in  this  instrument,  while  the  loss  occasioned  by  radiation 
from  tlie  blackened  surface  which  receives  the  concenti-ated 
radiant  heat  has  been  reduced  to  a  mere  fi'action.  It  may  be 
contended,  however,  that  tlie  loss  by  radiation  of  the  heater 
against  the  interior  surface  of  the  calorimeter,  although  minute, 
is  yet  appreciable,  and  that  some  heat  will  be  lost  by  conduc- 
tion at  the  points  where  that  vessel  joins  the  surrounding 
chambers.  Even  these  trifling  sources  of  erroi',  it  will  l^e  seen 
presently,  have  been  removed  by  the  new  method.  A  force- 
pump  and  a  cistern  containing  water  maint<ained  at  a  constant 
temperature  of  60°  F.  are  arranged  near  the  calorimeter.  By 
means  of  this  ]iump  and  the  flfxilile  pipes  before  referred  to, 
a  constant  ciin-ent  is  kept  up  through  the  space  between  the 
internal  and  external  casings  of  the  instrument ;  hence  the 
materials  composing  the  lattei-  may  quickly  be  brought  to 
the  same  temperature  as  the  cii'culating  watei'.  The  process 
of  measuring  the  radiant  energy  is  conducted  in  the  following 


100  KABJANT  HEAT.  CHAP.  v. 

maimer:  The  tliciiiKuiieter  being  witlulrawn,  tlie  cvliiidrical 
vessel  <>i'  licatiT  is  cliarged  with  distilled  \vater  of  a  tempe- 
rature of  al)<)iit  45°  F.,  after  whieli  the  thermometer  is  again 
inserted  and  the  instrument  exposed  to  the  sun,  the  paddle- 
wheel  ])eing  kept  in  motion.  The  indication  of  the  thermo- 
meter must  then  be  watched,  and  the  time  accurately  noted 
Avhen  the  mercurial  column  marks  50°  on  the  scale,  the  obser- 
vation continuing  until  the  thermometer  marks  70°,  at  Avhieh 
point  tile  time  is  again  accurately  noted.  The  experiment 
being  then  concluded,  the  lens  should  be  covered.  The  cir- 
culating water  being  kept  at  a  constant  temperature  of  60° 
F.,  it  scarcely  needs  explanation  that,  during  the  elevation  of 
the  temperature  of  the  water  from  50°  to  60°,  the  instrument 
radiates  fowarJn  (lie  lieater  /  and  that,  while  the  temperature 
rises  from  60°  to  70°,  the  heater  radiates  towanh  the  instni- 
mevt.  In  each  case  the  amount  of  heat  radiated  and  received 
is  almost  inappreciable,  since  the  vessel  containing  the  water 
to  be  heated  and  the  surrounding  vessel  are  composed  of 
highly  polished  metal.  The  amounts  of  gain  and  loss  of  heat 
by  conduction  at  the  points  Avliere  the  heater  is  joined  to  the 
external  vessel,  if  appreciable,  evidently  balance  each  otlier 
in  the  same  manner  as  the  gain  and  loss  by  radiation. 

The  weight  of  distilled  water  at  60°  contained  in  the 
heater,  and  the  weight  and  specific  heat  of  the  materials 
which  compose  its  parts,  being  ascertained,  tlie  number  of 
thermal  units  necessary  to  elevate  the  temperature  of  the 
whole  20°  F.  may  be  readily  calculated.  To  this  must  be 
added  the  percentage  of  calorific  energy  lost  dui'iiig  the  pas- 


CHAi-.  V.      MEVIIAMCAL  EKEUCY  OF  SOLAE  TiAI>TATION.  101 

sage  of  the  sun's  rays  tluough  the  lens.  The  sum  will  repre- 
sent a  permanent  coefficient  foi-  each  particular  instrument. 
Obviously,  the  indication  of  the  solar  calorimeter  will  not  be 
less  reliable  during  winter  in  a  northern  latitude,  with  the 
mercury  at  zero,  than  duiing  summer  within  the  tropics,  when 
the  thermometer  marks  100°  in  the  shade.  Noi-  must  it  be 
supposed  that  the  same  difficulty  presents  itself  in  ascei-tain- 
ing  the  loss  of  energy  of  the  rays  of  heat  as  that  involved 
in  a  determination  of  the  retardation  A\hich  rays  of  light 
suffer  during  their  passage  through  a  lens.  In  order  to  deter- 
mine the  former,  we  have  only  to  comjiare  the  units  of  heat 
developed  by  the  direct  action  of  a  pencil  of  rays  of  a  given 
section  with  the  number  of  units  developed  by  another  pencil 
of  equal  section,  acting  during  an  equal  interval  and  at  the 
mme  time,  through  the  lens  the  retaiding  influence  of  which 
we  desire  to  ascertain. 

The  weight  of  water  contained  in  the  heater  of  the  solar 
calorimeter  employed  during  the  investigations  refen-ed  to  in 
this  work  is  0.8125  11).  avoirdupois,  the  weight  of  the  materials 
composing  the  heater,  paddle-wheel,  and  other  parts  l>eing 
0.20.8  lb.  As  the  specific  heat  of  these  materials  is  0.12"),  it 
will  be  evident  that  0.125  X  0.298  =  0.0;?72  lb.  should  be 
added  to  the  weight  of  water  contained  in  the  heater.  Ac- 
cordingly, the  total  weight  will  amount  to  0.8125  +  0.0.'i72 
=  0.8497  lb.  The  elevation  of  temperature  in  the  heater 
l)eing  fi.ved  at  20^  F.,  it  will  be  seen  that  the  dynamic  enei-gy 
developed  during  each  experiment  will  ;tmount  to  20  X  0.8497 
=   1G.994  tlwrmal  units,  besides  the  energy  absorbed  l)y  the 


102  RADIANT  HEAT.  citai'.  V. 

lens,  wliicTi,  agreea1)]y  to  actual  trial,  amounts  to  very  nearly 
0.10.  Consequently,  0.10  X  16.994  +  16.994  =  18.6934  ther- 
mal nnits  represent  a  permanent  coefficient  of  energy  for  the 
particular  instrument  referred  to.  Let  us  clearly  understand 
that,  at  the  conclusion  of  each  experiment,  whatever  be  the 
time  occupied  in  attaining  the  stii)ulated  20°  F.,  the  stated 
amount  of  energy,  viz.,  18.6934  thermal  units,  has  been  deve- 
lojied.  We  are,  therefore,  enabled  to  determine  the  amount 
of  mechanical  energy  developed  by  solar  radiation  at  the  sur- 
face of  the  earth  by  observing  the  time  occupied  in  attaining 
the  stipulated  temperature,  and  then  dividing  the  coefficient 
of  energy  by  the  time  thus  observed.  But  it  will  be  per- 
ceived, on  reflection,  that,  in  order  to  solve  the  important 
problem  of  solar  emission,  the  following  conditions  must  be 
fulfilled  at  the  time  of  conducting  the  experiment :  (1)  The 
sun  must  be  perfectly  clear.  (2)  The  position  of  the  earth 
in  the  orbit  must  be  knoAvn  in  order  to  enable  lis  to  deter- 
mine the  distance  of  the  sun  and  the  consequent  dispersion 
of  the  rays  during  the  observation.  (3)  The  sun's  zenith 
distance  must  be  known,  since  the  loss  of  radiant  energy 
by  absorption  depends  on  the  depth  of  atmosphere  pene- 
trated by  the  rays.  The  second  and  third  of  these  condi- 
tions are  of  course  readily  met ;  but  the  first  condition  can 
only  be  fulfilled  by  repeating  the  observations  during  a 
series  of  years  whenever  the  sun  is  exceptionally  clear.  The 
writer  feels  confident  that,  by  having  adopted  this  system, 
the  problem  of  solar  emission  has  been  satisfactorily  solved. 
An  account  of  the  observations  successively  made  being  devoid 


cu.U'.  V.      MEVUAyiCAL  ENEliGT  OF  SOLAR  RADIATION.  103 

of  interest,  it  will  be  suflicieut  to  state  that  the  observed 
maximum  solar  intensity  occurred  March  7,  1871,  the  sun 
beiuo-  then  so  clear  that  the  before-mentioned  amount  of 
18.6934   thermal    units    was  developed    in    10    min.    0.5    sec, 

hence  — '- =  1.8678    units    per    minute.     The    sectional 

10.00833  ^ 

area  of  the  pencil  of  rays  entering  the  solar  calorimeter  wa.", 
as  already  stated,  0.37187  square  foot.  Consequently,  if  we 
reduce  the  foregoing  elements  to  the  usual  standard — one 
square  foot  of  area  acted  tipo7i  by  the  sun  in  one  minute — 
it  will  be  found  that,  on  the  occasion  I'eferred  to,  an  energy 
of  5.03  units  of  heat  per  minute  was  developed  by  a  pencil 
of  solar  rays  of  1  square  foot  section.  The  mean  zenith  dis- 
tance during  the  experiment  was  46  deg.  5  rain.,  -while  the 
position  of  the  earth  in  the  orbit  was  such  that  the  sun's  rays 
suffered  a  dispersion  of  45,400  to  1.  Keferring  to  the  table  of 
temperatures  for  given  zenith  distances  (see  page  62),  it  will 
be  found  that  the  radiant  intensity  at  46  deg.  5  min.  zenith  dis- 
tance is  diminished  in  the  ratio  of  67°.2  :  59°.85.  The  energy 
developed  by  oui-  calorimeter  during  the  experiment  was,  of 
coui-se,  reduced  in  the  same  proportion.  Introducing,  then, 
the  necessaiy  correction  for  the  stated  loss  caused  by  zenith 
distance — i.e.,  atmospheric  absorption— the  tnie  energy  deve- 
loped by  the  radiation  at  the  surface  of  the  earth  during  the 

67.20  X  5.03        .^^        .^  .     ,        p^ 

experiment  was  — — =  o.64  units  per  minute.  Ke- 
ferring to  Chap.  III.,  it  will  be  found  that  the  temperature 
produced  by  solar  radiation  at  the  boundary  of  the  terrestrial 


104  B AVIAN!  HEAT.  chap.  V. 

atiuospliere  is  U.207  greater  tbau  that  developed  near  the  siir- 
faee  of  the  earth ;  in  other  words,  the  eneigy  absorbed  b}- 
the  atmosphere  is  to  that  transmitted  to  the  eai-th  as  0.207  : 
0.793.  Consequently,  the  energy  develojied  by  solar  radia- 
tion at  the  boundary  of  the  atmos^phere,  March  7,  1871,  was 

5.64  WIT-  !■  ,  J5  P 

=  7.11  thermal   units  ou  one  square  toot  of  suriace  ; 

0.793  ^ 

while  the  dispersi<,)u  of  the  rays  on  that  day  was  in  the  ratio 
of  45,400  to  1.  It  needs  no  demonstration  to  prove  that, 
according  to  this  ratio  of  dispersion  of  the  rays,  the  energy 
emanating  from  one  square  foot  of  the  photosphere  must 
heat  45,400  square  feet  of  surface  at  the  boundary  of  the 
teri'estrial  atmosphere.  Our  investigation  having  shown  that 
solai"  radiation  develops  an  energy  of  7.11  units  to  the  square 
foot  on  entering  the  terrestrial  atmosphere,  it  follows  that 
solar  emission  amounts  to  45,400  X  7.11  =  322,794  thermal 
units  in  one  minute  for  each  square  foot  of  the  photosphere. 
In  view  of  the  completeness  of  the  means  adopted  in  mea- 
suring the  energy  developed,  and  the  ample  time  which  has 
been  devoted  to  the  determination  of  maximum  intensity,  it 
is  not  probable  that  future  labors  will  change  the  result  of 
our  investigation.  The  continuous  shrinking  of  the  sun  will 
produce  a  perceptible  diminution  of  the  radiant  energy  trans- 
mitted to  the  earth  in  the  course  of  a  few  hundred  centuries, 
but  the  emissive  energy  for  a  given  area  of  the  sun  \vill  remain 
constant  for  millions  of  years,  since  the  intensity  developed 
by  the  falling  mass  will  increase  inversely  as  the  square  of 
its  distance  from  the  solar  centre,  thus  balancing  the  dinii- 


CHAP.  T.    MKcn.iMCAL  i:.\i:i;ay  oFsoLAi:  i:ai>i.\ti<)x.         loo 

uutiou    of    energy    consequent    on    the    rediicecl    fall   of    the 
mass. 

The  illustration  sliowu  on  Platte  11  represents  a  vertical 
section  of  a  portable  solar  calorimeter,  in  all  essential  features 
similar  to  the  instrument  descrihed  in  the  present  chapter, 
the  only  material  ditVerence  l)eing  that  of  employing  a  W^- 
actimj  circulating  \vheel  within  the  heater.  Referring  to  the 
illustration,  it  will  lie  seen  that  the  instrument  is  placed  on 
an  ordinary  table,  a  weight  being  suspended  under  the  same 
for  actuating  the  circulating  wheel.  The  cylindrical  chamber 
which  contains  the  heater  moves  on  a  hinge  secured  to  a 
circular  bed-plate  i^rovided  with  cogs,  turning  round  a  ver- 
tical pivot  fastened  to  the  top  of  the  table,  the  inclination 
being  regulated  by  a  tangential  screw.  A  horizontal  pinion, 
geared  into  the  cogged  bed-plate  referred  to,  enables  the  ope- 
rator to  follow  the  diurnal  motion,  while  the  tangential  screw 
enables  him  to  regulate  the  inclination  of  the  lens  with  refe- 
rence to  the  sun's  declination.  Appropriate  sights  are  applied 
to  the  front  side  of  the  cylindrical  chambei',  showing  when 
its  axis  points  tow-ards  the  sun's  centre,  while  a  graduated 
(piadrant  indicates  the  zenith  distance  at  all  times.  It  will 
l)e  found,  by  inspecting  the  illustration,  that  the  axle  of  the 
bai-rel  actuated  by  the  motive  weight  is  connected  by  a  train 
of  cog-w^heels  to  the  shaft  of  the  circulating  wheel  within 
the  heater.  The  perfect  regularity  of  rotation  imparted  to 
this  wheel,  and  the  consequent  perfectly  uniform  circulation 
kept  up  within  the  heater,  dispenses  with  the  necessity  of 
exhausting  the  air  from  the  cylindrical  chamber,  on  the  fol- 


100  RADIANT  HEAT.  CHAP.  v. 

lowing  grounds  :  The  beat  imparted  by  the  air  \vithin  the 
chamber  during  the  fii'st  half  of  the  experiment  balances  the 
heat  absorbed  during  the  second  half.  There  is  a  difference, 
but  too  small  to  cause  an  appreciable  error.  It  may  be  men- 
tioned that  the  portable  solar  calorimeter  thus  described  was 
originally  constructed  for  ascertaining  the  dynamic  energy 
developed  by  solar  radiation  on  the  plains  of  India  and  in 
xViisti'alia.. 


CHAPTER    VI. 


THERMAL  ENERGY   TRANSMITTED   TO   THE   EARTH    I'.Y 

RADIATION  EROi[  DIFFERENT  PARTS  OF  THE 

SOLAR  SURFACE. 


Pere  Secchi,  in  the  second  edition  of  "  Le  Soleil,"  pub- 
lislied  at  Paris,  1875,  calls  special  attention  to  tlie  result  of 
his  early  investigations  of  the  force  of  radiation  emanating 
from  different  regions  of  the  sun's  surface,  reiterating  with- 
out modification  his  former  opinions  regarding  the  absorption 
of  the  radiant  heat  by  the  solar  atmosphere.  It  will  be  well 
to  bear  in  mind  that  the  plan  adopted  by  the  Italian  physi- 
cist in  his  original  researches,  on  which  his  present  opinion  is 
based,  was  that  of  projecting  the  sun's  image  on  a  screen, 
and  then,  by  means  of  thermopiles,  measuring  the  tempera- 
ture at  different  points.  The  serious  defects  inseparable  from 
this  method  of  measuring  the  intensity  of  the  radiant  heat 
I  need  not  point  out,  nor  Avill  it  be  necessary  to  urge  that 
a  correct  determination  of  the  energy  transmitted  calls  for 
direct  observation  of  the  temperature  produced  by  the  rays 
projected  towards  the  earth.     Accordingly,  on  taking  up  that 


108  EAVIANT  HEAT.  CHAP.  VI. 

brancli  of  my  investigations  of  radiant  licat  which  relates  to 
the  difference  of  intensity  transmitted  from  different  parts  of 
the  sun's  surface,  T  adopted  the  method  of  direct  observation. 
The  progress  was  slow  at  the  beginning,  owing  to  the  neces- 
sity of  constructing  an  astronomical  apparatus  of  unusual 
dimensions  ;  but  having  devised  means  which  rendered  the 
employment  of  any  desirable  focal  length  easy,  the  work  has 
progressed  rapidly.  An  instrument  of  17.7  metres  (58  feet) 
focal  length,  erected  to  conduct  preliminary  experiments,  has 
proved  so  satisfactory  that  the  construction  of  one  of  30  metres 
focal  length,  which  I  supposed  to  be  necessaiy,  has  been  dis- 
pensed with.  Considering  that  the  apparent  diameter  of  the 
sun  at  a  distance  of  17.7  metres  from  the  observer's  eye  is 
162.4  millimetres,  even  when  the  earth  is  in  aphelion,  the 
efficacy  of  the  instrument  employed  might  have  been  antici- 
pated. The  nature  of  the  device  will  be  readily  comprehend eil 
by  the  following  explanation:  Suppose  a  telescopic  tube  17.7 
metres  long,  1  metre  in  diameter,  devoid  of  object-glass  and 
lenses,  and  mounted  equatorially,  to  be  closed  at  both  ends 
by  metallic  plates  or  diaphragms,  at  right  angles  to  the  tele- 
scopic axis  ;  suppose  the  diaphragm  at  the  upper  end  to  be 
perforated  with  two  circular  apertures  200  millimetres  in 
diameter,  situated  one  above  the  other  in  the  vertical  line, 
3 GO  millimetres  from  centre  to  centre  ;  and  suppose  a  third 
circular  perforation  whose  area  is  one-fifth  of  the  apparent 
area  of  the  solar  disc — viz.,  72,6  millimetres  diameter — to  be 
made  on  either  side  of  the  vertical  line ;  suppose,  lastly, 
that  the  diaphragm  wliich  closes  the  lower  end   of  the   tube 


CH.VP.  vr.  UNEQUAL  UADIATIOX  OF  SOLAR  DISC.  109 

be  pei-forated  witli  three  snmll  apertures  0  luilliinetres  in  dia- 
meter, whose  centres  correspond  exactly  with  the  centres  of 
the  three  large  perforations  in  tlie  upper  diaphragm.  The 
tube  being  then  dii-ccted  tuwaiils  tlie  sun,  and  actinometers 
applied  below  the  thi'ee  small  apertures  in  the  lower  dia- 
phragm, it  will  be  evident  that  two  of  tliese  instruments  will, 
after  due  exposure  to  a  clear  sun,  indicate  maximum  solar 
iutensiity,  say  3;")°  C,  while  the  actinometer  applied  in  line 
with  the  perforation  whose  area  is  one-fifth  of  the  apparent 

area  of  the  solar  disc   will   indicate  —  =   7°  C,  unless  the 

central  portion  of  the  solar  disc  radiates  more  powerfully 
towards  the  earth  than  the  rest,  in  which  case  a  higher  inten- 
sity than  7°  C.  "will  be  indicated  by  the  actinometer  referred 
to.  It  will  be  readily  understood  that  the  solar  rays  entering 
thi'ough  the  perforations  at  the  upper  end  of  the  tube  con- 
verge at  the  low^er  end  and  pass  through  the  small  perfora- 
tions, causing  maximum  indication  of  the  focal  actinometera 
as  stated.  Now,  suppose  that  a  circular  plate,  the  area  of 
which  is  exactly  four-fifths  of  the  appai'ent  area  of  the  sun — 
viz.,  145.2  millimetres  diameter — be  inserted  concentrically  in 
either  of  the  two  large  perforations  of  the  diaphragm  at  the 
top  of  the  telescopic  tul)e.  The  apparent  diameter  of  the 
sun  being,  as  before  stated,  1G2.4  millimetres,  it  will  be  per- 
ceived that  the  inserted  plate  will  only  pai-tially  exclude  the 
solar  radiation,  and  that  the  rays  from  a  zone  1'  42"  wide 
will  pass  outside  the  said  plate,  converging  in  the  form  of 
a  hollow  cone  at  the  lower  end  of  the  tulte,  and  there  enter 


110  RADIANT  HEAT.  CHAP.  VI. 

the  respective  actiuometer.  The  iudicatiou  of  the  latter  will 
then  show  the  thermal  energy  transmitted  by  radiation  from 
a  zone  whose  mean  width  extends  49"  from  the  sun's  border. 
It  should  be  particulai'ly  observed  that  the  three  focal  acti- 
nometers  employed  will  be  acted  upon  simtdtaneously  by  the 
converged  I'ays,  (1)  from  the  entire  area  of  the  solar  disc, 
(2)  from  a  central  region  containing  one-fifth  of  the  area, 
and  (3)  from  a  zove  at  the  border  containing  also  one-fifth 
of  the  area  of  the  solar  disc.  It  is  scarcely  necessary  to 
point  out  that  an  accurate  comparison  of  the  intensity  of  the 
radiant  heat  emanating  from  the  central  pai't  and  from  the 
sun's  border  calls  for  simtdtaneovs  observation,  in  order  to 
avoid  the  errors  resulting  from  change  of  zenith  distance  and 
variation  of  atmospheric  absorption  during  the  investigation. 
The  great  advantage  of  obtaining  also  a  simultaneous  indica- 
tion of  the  intensity  transmitted  by  radiation  from  the  entire 
solar  disc  is  self-evident,  since  this  indication  serves  as  an 
effectual  check  on  the  observed  intensities  emanating  from 
the  centre  and  from  the  harder.  The  latter  obviously  must 
be  less,  while  the  former  must  be  greater,  for  a  given  area, 
than  the  indication  of  the  focal  actiuometer  which  receives 
the  radiation  of  the  entire  solar  disc. 

The  foregoing  demonstration,  based  on  h}'pothesis,  having 
established  the  possibility  of  ascertaining  by  direct  observa- 
tion the  temperature  produced  by  the  rays  projected  from 
certain  parts  of  the  solar  surface,  let  us  now  examine  the 
means  actually  employed.  An  observer  on  the  40th  deg. 
latitude,  stationed  on  the  north  side  of  a  building  28  metres 


CHAP.  VI.  UXEQUAL  FADTATTOX  OF  SOLA!.'  DfSC.  m 

liigli,  pointing  east  and  west,  can  just  see  the  sun  pass  the 
meridian,  duiing  the  sunmier  s<il.«tice,  if  he  occu2>ies  a  posi- 
tion about  8  metres  fi'om  such  buihling.  Kow,  if  an  opaque 
screen,  perforated  by  a  circuhir  opening  .".1."')  niillinieti-es  in 
diameter,  be  placed  on  the  top  of  tlie  su])po.';ed  building,  the 
entire  solar  disc  may  be  seen  through  the  same,  pro\nded  it 
faces  the  sun  at  right  angles.  But  if  the  pei-foration  in  the 
said  screen  be  140  millimetres  in  dianietci-,  only  one-fifth  of 
the  area  of  the  solar  disc  will  be  seen.  And  if  the  screen  be 
removed  and  a  circular  plate  280  millimetres  in  diameter  put 
in  its  place,  the  observer,  ranging  himself  in  line  with  the  plate 
and  the  sun's  centre,  can  see  only  a  narrow  border  1'  42"  of 
the  solar  disc.  Obviously  the  screen  placed  on  the  io-p  of 
the  building  might  be  perforated  lil:e  the  upjier  diaphragm 
of  the  supposed  telescopic  tube,  and  a  plate  resembling  the 
lower  diaphragm,  secured  by  apjiropriate  means  near  the 
ground,  might  be  made  to  support  the  focal  aotinometers  in 
such  a  manner  that  their  axes  pass  through  the  centres  of 
the  perforations  of  the  screen  above  the  building.  It  is 
hardly  necessarj'  to  state  that  the  plate  supporting  the  aoti- 
nometers should  be  attached  to  some  mechanism  capable  of 
imjiarting  to  it  a  parallactic  movement,  during  the  observa- 
tion, corresponding  with  the  sun's  declination  and  the  earth's 
diurnal  motion,  and  that  some  adequate  mechanism  should 
be  employed  for  regulating  the  position  of  the  perforated 
screen  and  adjusting  the  focal  distance  in  accordance  vaih 
the  change  of  the  subtended  angle  consequent  on  the  vary- 
ing  distance  from   the   sun.      It  will   be  evident   that,  since 


113  liADIANT  HEAT.  chap.  vi. 

the  first-iiauieJ  mecluiiiisiu  rests  on  tLe  ground,  wliile  tlie 
latter  is  secured  to  a  massive  building,  far  greater  steadi- 
ness will  be  attained  by  our  simple  and  comj^aratively  inex- 
[)ensive  device  tlian  by  employing  a  telesco^iic  tube  of  the 
most  perfect  construction  mounted  equatorially. 

Witli  reference  to  tlie  influence  of  diffraction,  it  should 
be  stated  tliat,  before  deteiiuining  the  size  of  the  screens  in- 
tended to  shut  out  cei-tain  parts  of  the  soLnr  disc  during  the 
investigation,  the  amount  of  inflection  of  the  sun's  rays  was 
carefully  ascertained.  Two  distinct  methods  were  adopted  : 
(1)  measuring  the  additional  amount  of  heat  transmitted  to 
the  focal  thermometers  in  consequence  of  the  inflection  of 
the  rays ;  (2)  increasing  the  tlieoretical  size  of  the  screens 
until  the  effect  of  inflection  was  overcome  and  the  luminous 
rays  completely  excluded.  Regarding  the  first-named  method 
of  ascertaining  the  diffraction,  it  is  important  to  mention  that 
the  temperature  transmitted  to  the  focal  actinometers  by  the 
inflected  radiation  which  passes  outside  of  the  theoretically 
determined  screens  is  not  proportionate  to  the  inflection  ascer- 
tained by  the  process  of  enlargement  referred  to.  This  cir- 
cumstance at  first  rendered  the  investigation  somewhat  com- 
plicated, but  it  soon  became  evident  that  the  discrepancy  was 
caused  by  tlie  comparatively  small  inflection  of  the  invislhh 
heat  rays.  It  will  Ije  seen  jiresentlj^  that  the  radiant  heat 
which  passes  outside  of  the  screens  in  consequence  of  diffrac- 
tion is  considerably  less  than  that  which  -would  be  transmitted 
to  the  focal  actinometers  if  the  calorific  rays  ^vel•e  sulijected 
to  an  amount  of  inflection  corresponding  with  the  enlargement 


CUAP.  VI.  UNEQUAL  HAI'IATIOX  OF  SOLAR  DISC.  113 

of  the  screens  beyoucl  the  tbeuietical  dimeusious  uecessaiy  to 
excliule  tLe  luminous  rays. 

Let  us  first  consider  the  metht)d  of  ascertaining  the  inflec- 
tion of  the  rays  by  measuring  the  additional  amount  of  heat 
transmitted  to  the  focal  actinometers.  Fig.  1  (see  Plate  12) 
represents  the  solar  disc,  a  being  the  focal  actinometer  exposed 
to  the  converged  rays,  a'  a'  representing  an  imaginary  plane 
situated  17.7  metres  from  a,  at  which  distance  the  section  of 
the  pencil  of  converging  rays  will  be  162.4  millimetres  in 
diameter,  provided  the  earth  is  near  aphelion.  Fig.  2  also 
represents  the  solar  disc,  and  c  the  actinometer  exposed  to 
the  converged  rays ;  but  a  perforated  screen  b'  b'  is  intei-posed, 
the  perforation  being  of  such  a  size  that  only  the  rays  pro- 
jected by  the  central  half  of  the  solar  disc  (indicated  by  the 
circle  h  />)  pass  through  the  same  and  reach  the  focal  actino- 
meter. The  screen  b'  b'  being  situated  17.7  metres  from  c 
M-heu  the  earth  is  in  the  position  before  referred  to,  the  said 
perforation  must  be  114.83  millimetres  in  diameter,  in  order 
that  the  lines  b  x'  c  may  be  straight.  Fig.  3  likewise  repre- 
sents the  solar  disc,  its  area  being  divided  into  two  concentric 
halves  by  the  circle  d  d  ;  but,  in  place  of  a  perforated  screen, 
an  opaque  circular  screen  d'  is  introduced  at  the  same  distance 
from  the  focal  actinometer  as  in  Fig.  2  ;  consequently,  the  lines 
d  y'  f  ^vill  be  straight.  Now,  if  the  actinometei-s  a,  c,  and  / 
be  exposed  to  the  converged  solar  radiation  simultaneously 
and  during  an  eqval  interval  of  time,  c  and  /  receiving  the 
heat  from  one  half  of  the  solar  disc  (the  former  from  the 
central  and  the  latter  from  the  sun-ounding  half),  the  tempe- 


114  RADIANT  HEAT.  chap.  vi. 

ratures  of  c  and  /  added  together  should  coiTesjDoud  exactly 
with  the  temperature  transmitted  from  the  entire  solar  disc 
to  a.  Observation,  however,  shows  that  the  temperature  of 
c  and /together  is  0.091  greater  than  the  temperature  imparted 
to  a.  Hence  an  increase  of  temperature  of  nearly  one-eleventh 
is  produced  by  the  inflection  of  the  calorific  rays,  one-half 
being  the  result  of  the  bending  of  the  rays  vnthin  the  per- 
foration of  the  screen  h'  h',  the  other  half  resulting  from  the 
bending  outside  of  the  screen  d'.  The  increment  of  tempe- 
rature being  thus  known,  the  degree  of  inflection  may  be 
easily  determined  by  drawing  a  circle  x  x  round  the  circle 

7   7  •  •,-...-,  „  0.091 

0  b,  covermg  an  additional  area  of =  0.0455;   and  by 

inscribing  a  circle  y  y  within  d  d,  covering  an  area  of  0.0455 
less  than  the  area  of  d  d.  It  will  be  perceived,  on  reflection, 
that  X  x'  b  represents  the  angle  of  inflection  of  the  calorific 
rays  within  the  perforation  of  the  screen  b'  b',  and  that  d  y'  y 
represents  the  angle  of  inflection  outside  of  the  screen  d'. 
Demonstration  shows  that  the  former  angle  measures  14".57, 
while  the  latter  measui-es  14".86,  the  mean  being  ]4".7l. 
Having  thus  determined  the  inflection  resulting  fi-om  invi- 
sible radiation,  let  us  now  ascertain  the  inflection  of  the 
luminous  rays.  As  before  stated,  the  apparent  diameter  of 
the  sun  at  a  distance  of  17.7  metres  from  a  given  point  is 
162.4  millimetres  when  the  luminary  is  fui-thest  from  the 
earth.  Now,  our  investigation  shows  that  a  screen  167  milli- 
metres in  diameter   hardly  sufiices  to  exclude  the  luminous 

1            ^1    ■     ■  a    .■                              167  -  162.4 
rays ;    hence  their  inflection  amounts  to  =  2.3 


CHAP.  VI.  UXEQUAL  EADIATIOy  OF  SOLAR  DISC.  115 

millimetres  in  a  length  of  17.7  metres.  Their  angle  of  inflec- 
tion \vill  therefore  be  26".81,  against  14".71  for  the  dark  rays. 
We  have  thus  incidentally  established  the  fact  that  the  inflec- 
tion of  the  luminous  and  calorific  rays  differs  nearly  in,'  the 
same  proportion  as  the  calorific  energies  of  the  invisible  and 
visible  portions  of  the  solar  spectrum. 

The  illustration  on  Plate  13  represents  a  top  view  (see 
Fig.  15)  and  a  transverae  section  (see  Fig.  17)  of  the  paral- 
lactic mechanism  employed  in  the  investigation.  The  leading 
feature  of  the  device  is  that  of  attaching  three  actinometers, 
f,  Ji,  and  (/,  to  a  plate  which  may  be  set  at  any  desired 
inclination,  and  capable  of  being  moved  simultaneously  at 
right  angles  to,  and  in  a  direction  parallel  vpith,  the  meri- 
dian. The  mode  of  effecting  this  movement  will  be  readily 
understood  by  the  following  description,  reference  being  had 
to  the  illustration :  a  is  a  screw,  the  threads  of  which  are 
foi-med  to  a  pitch  of  three-eighths  of  an  inch,  placed  hori- 
zontally and  at  right  angles  to  the  meridian,  the  ends  turn- 
ing in  bearings  bolted  to  a  substantial  frame  /;  ?>,  supported 
by  legs  resting  on  a  solid  stone  foundation.  A  radial  arm 
c,  the  position  of  which  is  regulated  by  a  graduated  quadrant 
c',  is  fastened  to  the  end  of  the  screw  a;  the  latter  being 
by  that  means  prevented  fi-om  turning  round,  d  J,  arms  con- 
nected by  a  cylindrical  socket  d',  which  slides  freely  back 
and  fonvards  on  the  screw.  The  said  socket  is  prevented 
from  turning  round  the  screw  by  the  application  of  a  square 
key  a',  fitted  accurately  into  a  rectangular  longitudinal  groove 
formed  in  the  side  of  the  screw,     e  e,  plate  sliding  between 


116  RADIANT  HEAT.  chap.  vi. 

appropriate  guide-rods  secured  to  the  ujiper  side  of  tlie  arms 
d  d,  motion  being  imparted  to  this  plate  by  a  micrometric 
screw  e'.  The  actinometers  /,  (/,  and  h  are  attached  to  a 
plate  I;  bolted  to  the  top  of  e  e.  The  sliding  socket  d'  is 
moved  along  the  main  screw  by  a  milled  nut  /,  held  against 
the  end  of  the  said  socket  by  a  forked  piece  I'  fastened  to 
the  arm  d  and  acting  on  a  collar  formed  at  the  small  end 
of  the  milled  nut.  It  scarcely  needs  explanation  that,  by 
turning  this  nut,  the  sliding  socket  d'  may  be  made  to  move 
along  the  main  screw  in  either  direction,  thereby  imparting 
motion  to  the  plate  Js  which  supports  the  three  actinometers. 
Nor  will  it  be  necessary  to  demonstrate  that,  by  turning  the 
micrometric  screw  <?',  the  said  plate  may  be  moved  at  right 
angles  to  the  main  screw  a.  Consequently,  the  mechanism 
thus  described  enables  us  to  move  the  actinometers  with 
great  regularity  and  precision  across  the  meridian,  and  in  a 
direction  parallel  with  it.  By  means  of  a  flexible  tube  m  m, 
which  connects  the  surrounding  casings  of  the  three  actino- 
meters, a  stream  of  water  is  circulated  through  the  latter 
during  observations.  An  ordinary  force-pump  is  employed 
for  this  purpose,  attached  to  a  capacious  cistern  containing 
water  maintained  at  a  constant  temperature.  The  centres 
of  the  actinometers  /  and  (/  are  160  centimetres  apart,  a 
colored  glass  n  being  attached  to  the  jilate  7c  in  a  direct 
line  vsdth,  and  equidistant  from,  the  stated  centres.  An  eye- 
piece is  applied  to  the  colored  glass  w,  below  the  plate  k 
The  actinometers  are  provided  with  conical  apertures  on  the 
upper  side,  through  which  the  thermometers  are  introduced 


cn.vp.  VI.  Uy EQUAL  RADIATION  OF  SOLAR  DISC.  117 

when  the  instrument  is  in  operation.  In  the  illustration  these 
apei-tures  are  closed  by  conical  plugs  provided  with  globular 
handles.  Fig.  16  represents  a  square  bar  /•,  to  which  three 
circular  discs,  composed  of  sheet  brass,  are  attached  by  means 
of  deep  and  thin  arms,  foi-med  as  sho^vn  by  the  drawing. 
The  discs  /'  and  </'  are  placed  160  centimetres  apart,  fi-om 
centre  to  centre,  corresponding  exactly  with  the  distance 
between  the  axes  of  the  actinometers  /  and  ff ;  while  the 
centre  of  the  disc  s  con-esponds  with  the  centre  of  the  eye- 
piece below  the  colored  glass  n.  The  square  bar  r  is  held 
horizontally  and  at  right  angles  to  the  meridian  by  a  sub- 
stantial bracket  secured  to  the  top  of  some  building  of  ade- 
quate height ;  the  angular  position  of  the  bar  being  such 
that  it  corresponds  with  the  sun's  zenith  distance.  The  fi-ame 
b  h,  which  .supports  the  parallactic  mechanism,  rests  on  a  level 
stone  foundation,  its  distance  from  the  building  referred  to 
depending  on  the  season  and  the  latitude  of  the  place  of 
observation.  Assuming  that  the  bar  ;•,  which  supports  the 
discs  f,  s,  and  ;/',  has  been  correctly  placed,  and  that  the 
parallactic  mechanism  occupies  a  proper  position  on  the 
ground,  it  will  then  be  found  that,  when  the  sun  passes 
the  meridian,  the  disc  s  will  throw  a  small  round  shadow 
covering  the  colored  glass  n.  Obviously,  an  operator  lying 
on  his  back  under  the  frame  which  supports  the  instniment, 
with  his  right  hand  turning  the  milled  nut  I,  and  his  left 
luuul  turning  the  micrometric  screw  e',  will  be  enabled  to 
impart  a  simultaneous  right-angular  movement  to  the  acti- 
ii(»nit'tei-s.      Now,   the    diameter   of   the    flisc   s-  is   such    that, 


118  RADIANT  HEAT.  chap.  ti. 

when  brouglit  in  line  mth  the  sun  and  the  eye-jiiece  below 
n,  only  the  extreme  edge  of  the  solar  disc  is  seen  through 
the  colored  glass.  The  operator,  therefore,  by  careful  mani- 
pulation, may  readily  keep  the  eye-piece  and  the  disc  5>in 
line  with  the  solar  centre.  My  original  design  was  that  of 
actuating  the  parallactic  mechanism  by  clock-work ;  but, 
warned  by  the  frequent  failures  of  astronomers  to  keep  the 
sun  accurately  in  focus  even  during  the  short  period  of  an 
eclipse,  I  adopted  the  safer  method  of  operating  by  hand. 
The  distance  between  the  centres  of  the  discs  /'  and  g'  cor- 
responding exactly  with  the  distance  between  the  axes  of  the 
actinometers  /  and  g,  both  being  equidistant  from  the  axis 
of  the  eye-piece,  it  will  be  evident  that  the  centres  of  the 
discs  /'  and  g'  wlW  always  coincide  with  the  axes  of  their 
respective  actinometers  directed  towards  the-  solar  centre,  pro- 
vided the  operator  manipulates  the  instrument  so  carefully 
that  the  sun  is  kept  accurately  in  focus ;  in  other  words, 
that  no  distortion  is  suffered  to  take  place  of  the  annular 
face  or  narrow  border  of  the  sun  seen  through  the  colored 
glass.  It  hardly  needs  explanation  that  the  actinometer  h 
is  at  all  times  exposed  to  the  full  energy  of  the  converging 
rays  from  the  sun. 

As  a  detailed  account  of  the  result  of  the  investigation 
would  occupy  too  much  space,  the  leading  jjoiuts  only  will 
be  presented.  The  observations  have  all  been  made  at 
noon,  the  duration  of  the  exposure  to  the  sun  having  been 
limited  to  seven  minutes,  during  which  period  the  actino- 
meters are  moved,  by  the  parallactic  mechanism,  through  a 


CUAP.  VI.  UNEQUAL  RADIATION  OF  SOLAR  1)180.  119 

distance  of  about  55  centimetres,  from  west  to  east.  The 
intensity  of  the  radiant  heat  imparted  to  the  actinometers 
has  been  recorded  by  the  observers  at  the  termination  of 
the  fourth,  fifth,  sixth,  and  seventh  minute,  the  exact 
moment  for  reading  off  being  indicated  by  a  chronograph. 
The  relative  intensities  transmitted  by  radiation  from  the 
centre    and   from    the    border   of   the   solar    disc    first   claim 


our  attention.  Fig.  6  re2:)resents  the  solar  disc  covered  l)y 
a  circular  screen  145.25  millimetres  in  diameter,  excluding 
the  rays  excepting  from  a  narrow  zone,  the  mean  width  of 
which  is  situated  49"  from  the  border  of  the  photosphere. 
Fig.  7  shows  a  screen  excluding  the  solar  rays  excepting 
from  the  central  portion,  the  area  of  which  is  precisely  eqval 
to  the  area  of  the  narrow  zone  in  Fig.  6.  The  following 
table  shows   the   intensities  transmitted   to   the  actinometers 


130  BABIANT  HUAT.  chap.  vi. 

during  an  observatiou,  August  25,  1875,  the  radiation  from 
the  solar  disc  being  then  excluded  in  the  manner  shown  in 
Fis:s.  6  and  7. 


ime. 

Uentral  portion. 
Cent. 

£>orner. 

Cent. 

Rate  of  difference. 
2.19 

4' 

3°.28 

2°.19 

aas  -  »■<=''' 

5' 

3°.  56 

2°.37 

2.49 

6' 

3°.  73 

2°.49 

2.60 

7' 

3°.88 

2°.  60 

3.88  -  '■'^^ 
Mean  =  0.667 

It  should  be  particularly  observed  that  this  table  records 
the  result  of  four  distinct  observations  ;  nor  should  it  be  over- 
looked that  although  the  intensities  vary  greatly  for  each 
observation,  in  consequence  of  the  continued .  exposure  to  the 
sun,  yet  the  rates  shovdng  the  difference  of  the  intensity  of 
the  rays  transmitted  from  the  border,  inserted  in  the  last 
column,  is  pi-actically  the  same  for  each  observation,  the  dis- 
crepancy betvreen  the  highest  and  the  lowest  rate  being  only 
0.004.  It  should  be  mentioned  that  all  my  instruments  for 
measuring  radiant  heat  referred  to  in  this  work  have  been 
graduated  to  the  Fahrenheit  scale,  which  practically  is  more 
exact  than  the  Centigrade,  owing  to  its  finer  divisions.  For 
the  benefit  of  the  majority  of  readers  the  observed  tempera- 
tures have  been  reduced  to  Centigrade  scale  before  being 
entered  in   our  tables.      Persons  practically  acquainted  ^vith 


CHAP.  VI.  UNEQUAL  BADIATION  OF  SOLAR  DISC.  121 

the  difficulty  of  ascertaining  tlie  intensity  of  solar  radiation 
will  be  sui-prised  at  the  exactness  and  consistency  of  the 
indications  of  our  instruments.  This  desirable  exactness  has 
been  attained  by  surrounding  the  actinometers  with  ^\•ater- 
jackets,  which  communicate  with  each  other  by  connecting 
pipes,  through  which  a  steady  stream  of  water  is  circulated. 
By  this  expedient  the  chambers  containing  the  bulbs  of  the 
several  thermometers  are  maintained  with  critical  nicety  at 
equal  temperature — an  inexorable  condition  when  the  object 
is  to  determine  differential  temperature  with  great  exactness. 
Apart  from  this,  the  chambers  which  contain  the  bulbs  of 
the  thermometers  are  air-tight,  the  radiant  heat  being  admitted 
through  a  small  aperture  at  the  top  of  the  chamber,  covered 
by  a  thin  crystal. 

Referring  to  the  preceding  table,  it  ■will  be  seen  that  the 
intensity  transmitted  by  radiation  from  the  sun's  border,  repre- 
sented in  Fig.  6,  is  0.667  of  the  intensity  transmitted  from 
the  central  region  represented  in  Fig.  7,  the  area  of  each  being 
precisely  alike.  From  the  stated  intensity  must  be  deducted 
the  heat  imparted  to  the  actinometer  by  the  inflection  of  the 
calorific  rays.  The  circumference  of  the  perforation  of  the 
screen  sho^vn  in  Fig.  7  being  exactly  one-half  of  the  circum- 
ference of  the  screen  in  Fig.  6,  while  the  central  region  radi- 
ates more  powerfully  than  the  border,  fully  one-half  of  the 
inflected  radiation  from  the  border  will  be  balanced  by  the 
inflected  radiation  emanating  fi-om  the  central  region.  Agree- 
ably to  the  previous  demonstration  relating  to  Figs.  2  and  3, 
it  will   be   seen  that   the   unbalanced   inflection   amounts   to 


122  BABIANT  HEAT.  chap.  VI. 

0.029  ;  hence  tlie  radiation  transmitted  from  the  border  zone 
will  be  0.667  -  0.029  =  0.638  of  the  intensity  of  radiation 
transmitted  fi'om  the  central  region.  We  have  thus  shown 
by  a  reliable  method  that  the  intensity  of  the  rays  directed 
toAvards  the  earth  from  the  border  zone  suffers  a  diminution 
of  1.000  -  0.638  =  0.362  of  the  intensity  of  the  radiation 
emanating  from  the  central  region.  But  the  mean  depth  of 
the  solar  atmosphere  of  the  border  zone,  in  the  direction  of 
the  earth,  is  2.551  greater  than  the  vertical  depth,  while  the 
mean  depth  over  the  central  region  referred  to  is  only  0.036 
greater  than  the  vertical  depth  of  the  solar  atmosphere.  It 
will  be  evident  that  if  the  law  of  retardation  were  known, 
the  foregoing  figures  would  enable  us  to  determine  the  absorj)- 
tive  power  of  the  solar  atmosphere.  Concerning  this  law,  it 
should  be  mentioned  that  in  the  first  edition  of  "  Le  Soleil," 
page  264,  the  author  assumes  that  the  absorption  of  the  calo- 
rific rays  by  the  atmosphere  "  augments  in  proportion  to  the 
secant  of  the  zenith  distance " ;  in  other  words,  as  the  depth 
of  the  atmosphere  penetrated  by  the  rays.  Consequently,  if 
this  assumption  be  correct,  the  absorption  by  the  solar  atmo- 

0.362  „    , 

sphere  cannot  exceed   =  0.144  of  the  radumt 

^  2.551  -  0.036 

heat  emanating  from  the  photosphere.     It  will  be  found,  on 

referring  to  the  revised  edition  of  "  Le  Soleil,"  Vol.  I.,  p.  212, 

that  P6re  Secchi  makes  the  following  statements  regarding 

the  absorptive  power  of  the  solar  atmosphere :  (1)  "  At  the 

centre   of  the   disc — that   is   to  say,   perpendicularly  to   the 

surface  of  the  photosjihere — the  absorption  arrests  about  I, 


CHAP.  VI.  UNEQUAL  liADIATIOX  OF  SOLAR  DISC.  123 

or,  more  exactly,  tWt,  of  the  total  force."  (2)  "The  total 
action  of  the  absorbing  envelope  on  the  hemisphere  visible 
from  the  sun  is  so  great  that  it  allows  only  iSV  of  the  total 
radiation  to  pass,  the  remainder,  namely,  n'oV,  being  absorbed." 
It  is  unnecessary  to  criticise  these  figures  presented  by  the 
Eoman  astronomer,  as  a  cursory  inspection  of  our  table  and 
diagrams  is  sufficient  to  show  the  fallacy  of  his  computa- 
tions. Besides  determining  the  absoi-ptive  power  of  the  solar 
atmosphere,  another  impoi-tant  problem  may  be  solved  by 
accurately  measuring  the  intensity  of  the  radiation  emanat- 
ing fi'om  various  parts  of  the  disc — namely,  that  relating  to 
the  sun's  emissive  power  in  different  directions.  In  order 
to  decide  this  question,  I  have  adopted  the  plan  of  measur- 
ing the  energy  of  the  radiant  heat  transmitted  from  zones 
crossing  the  solar  disc  at  right  angles,  as  shown  in  Figs.  10 
and  11.  Repeated  observations  having  shown  that  the  acti- 
nometers  are  equally  affected  by  the  radiation  from  these 
zones,  each  of  which  occupies  an  arc  of  30  deg.,  containing 
one-third  of  the  area  of  the  disc,  the  inference  is  irresistible 
that  the  sun  emits  heat  of  equal  intensity  in  all  directions. 
It  should  be  borne  in  mind  that,  agreeably  to  our  method, 
the  radiations  from  these  zones  are  observed  simultaneously — 
a  fact  tending  to  prove  that  our  conclusions  cannot  be  erro- 
neous. The  arrangement  exhibited  in  Figs.  10  and  11  hardly 
needs  explanation.  Eef erring  to  Fig.  10,  it  will  be  seen  that 
two  segmental  screens  are  employed  excluding  the  radiant 
heat,  excepting  from  the  zone,  wliioh  is  inirallel  with  the 
sun's  equator.      Similar  screens  are  employed   (see  Fig.    11) 


124  BABIANT  HEAT.  chap.  VI. 

for  excludiug  tlie  rays  excepting  from  the  zone  j)ai"allel  "with 
the  sun's  polar  axis.  The  curvatures  of  the  segmental  screens, 
it  shoiild  be  observed,  have  been  struck  to  a  radius  of  ninety- 
millimetres,  in  order  to  cut  off  effectually  the  inflected  radi- 
ation from  the  sun's  border.  Obviously  diffraction  has  not 
called  for  any  correction  of  our  observations  relating  to  this 
part  of  the  investigation,  since  the  inflected  radiation  from 
the  equatorial  zone  exactly  balances  the  inflected  radiation 
from  the  polar  zone.  As  already  stated,  repeated  observa- 
tions show  that  the  radiant  energies  transmitted  to  the  acti- 
nometers  from  the  two  zones  are  identical. 

The  observations  relating  to  the  temperature  of  the  polar 
regions,  represented  in  Figs.  8  and  9,  at  first  led  to  the  sup- 
position that  the  rays  projected  from  the  north  pole  of  the 
sun  transmit  a  perceptibly  greater  energy  to  the  actinometers 
than  the  rays  from  the  opposite  pole.  Subsequent  observa- 
tions having  positively  established  the  fact  that  the  polar  and 
equatorial  zones  transmit  equal  intensities,  it  became  evident 
that  some  other  cause  than  difference  of  temperature  within 
the  polar  regions  influenced  the  actinometers.  The  only  valid 
reason  that  could  be  assigned  in  explanation  of  the  anomaly 
being  the  considerable  angle  subtended,  and  the  consequent 
difference  of  zenith  distance  of  the  opposite  poles  of  the  sun, 
my  table  of  maximum  solar  intensity  for  given  zenith  dis- 
tances (prepared  from  data  collected  during  a  series  of  years) 
was  consulted,  in  order  to  ascertain  the  influence  of  zenith 
distance.  The  observations  indicating  a  higher  temperature 
at  the  north  pole,   it  should  be  mentioned,  had  been  made 


CHAP.  VI.  UNEQUAL  HABIATIOX  OF  SOLAR  DISC.  125 

while  the  sun's  zenith  distance  I'anged  between  32  deg.  and 
33  deg.  at  noon.  Now,  the  table  i-eferred  to  shows  that  there 
is  a  difference  of  radiant  intensity  of  G3°.G3  —  G3°.40  =:  0°.23 
F.  between  the  stated  zeiiitli  distances.  Tlie  mean  angle  sub- 
tended by  the  sun  being  fully  thirty-two  minutes,  it  will  thus 
be  seen  that,  owing  to  the  absoi-ptive  power  of  the  terresti-ial 
atmosphere,  the  radiant  intensities  transmitted  from  the  oppo- 
site poles  of  the  luminary  dift'ei'  consideiably.  The  magni- 
tude of  this  difference,  adequate  to  explain  the  discrepancy 
under  consideration,  need  not  excite  surprise  if  we  consider 
that  thirty-two  minutes  of  zenith  distance  involves  an  addi- 
tional depth  of  more  than  half  a  mile  of  atmosphere  to  be 
penetrated  by  the  rays  projected  towards  the  actinometer  from 
the  south  pole  of  the  sun.  The  foregoing  facts  show  the  neces- 
sity of  taking  the  difference  of  zenith  distance  between  the 
opposite  poles  into  account  in  making  exact  observations  of 
the  sun's  polar  temjierature,  especially  at  the  lower  altitudes, 
where  the  secant  of  the  zenith  distance  increases  rapidly. 

Regarding  the  calorific  energy  of  the  radiation  emanating 
from  the  border  of  the  sun,  the  following  brief  statement 
presents  facts  of  considerable  importance  hitherto  unknown. 
Several  observations  during  the  early  part  of  the  investigation 
pointed  to  the  fact  that  increased  energy  is  transmitted  to 
the  actinometers  by  radiation  from  the  sun's  border.  Again, 
considerable  irregularity  was  observed  in  the  progressive  dimi- 
nution of  the  force  of  radiation  towards  the  circumference  of 
the  solar  disc.  It  has  already  been  shown  that  the  radiation 
from  the  border  zone,  1'  42"  wide,  occupying  one-fifth  of  the 


126 


RADIANT  HEAT. 


area  of  the  solar  disc,  transmits  0.638  of  the  intensity  trans- 
mitted from  an  equal  area  at  the  centre  of  the  disc.  Of 
course  it  will  be  supposed  that  the  rate  of  the  diminution 
of  intensity  within  the  zone  thus  ascertained  is  much  greater 
near  the  border  of  the  photosphere  than  at  the  middle  of 
the  zone.  Such,  however,  is  by  no  means  the  case,  notwith- 
standing the  assumption  of  physicists  that  the  heat  transmitted 
by  radiation  from  the  border  is  very  feeble.     In  order  to  test 


the  truth  of  the  indications  referred  to,  sho\ving  considerable 
radiant  energy  at  the  border  of  the  photosphere,  a  very  careful 
investigation  was  made,  Sept.  9,  1875,  by  means  of  screens 
excluding  the  rays  from  the  solar  disc,  as  shown  in  Figs.  12 
and  13.  The  diameter  of  the  screen  represented  in  Fig.  12, 
being  154.06  millimetres,  covered  nine-tenths  of  the  area  of 
the  disc ;  while  the  screen  shown  in  Fig.  18,  being  145.25 
millimetres,  covered  four-fifths  of  the  disc.  It  will  be  well 
to  mention  that   the  dimensions    of   the   screens  referred    to 


CHAP.  TI.  UNEQUAL  RADIATION  OF  SOLAR  DISC.  127 

correspond  to  the  angle  subtended  by  the  sun  Avben  the 
earth  is  in  aphelion.  Accordingly,  the  distance  between  the 
actinometers  and  the  screens  was  adjusted  previous  to  the 
obseiTation — that  is,  shortened — in  order  to  comiiensate  for 
the  increase  of  the  angle  subtended  by  the  sun.  Agreeably 
to  the  stated  dimensions  of  the  screens,  it  will  be  found  that 
the  zone  represented  in  Fig.  13  is  1'  42",  Avhile  the  zone  in 
Fig.  12  is  49".6.  The  mean  width  of  the  latter  is  conse- 
quently situated  only  2J:".3  from  the  border  of  the  photo- 
sphere. 

The  following  table  shows  the  intensities  transmitted 
to  the  actinometers  from  the  zones  represented  in  Figs.  12 
and  13: 

^"  Cent^'  ^"'  ^^  °^  Difference. 

„     "  1.333 

''■''"     1:1 = '■''' 

1°.583  ^^  =  0.652 

2.425 

7'  2°.485  1°.666  ]^  =  0.670 

2.485       

Mean  =  0.660 

The  rate  of  diflference  inserted  in  the  last  colmnn,  it  will 
be  noticed,  is  not  qiiite  so  consistent  as  in  the  table  recording 
the  observations  made  Aug.  25.  The  discrepancy  is,  however, 
not  material,  the  difference  between  the  lowest  and  the  mean 
rate  being  0.008.  It  will  be  seen,  on  inspecting  the  registered 
intensities,  that  the  border  zone  represented  in  Fig.  12,  whose 


Time. 

Cent. 

4' 

2°.011 

6' 

2°.  248 

6' 

2°.  425 

128  'RADIANT  HEAT.  chap.  vi. 

area  is  only  oue-lialf  of  tlie  area  of  tlie  zone  in  Fig.  13,  trans- 
mits 0.660  of  tlie  intensity  of  tlie  latter.  This,  at  fii'st  sight, 
indicates  an  extremely  disproportionate  transmission  of  heat 
from  the  narrow  border  zone ;  but  it  should  be  considered 
that  the  inflected  radiation  imparts  relatively  more  heat  to 
the  actinometer  exposed  to  the  radiation  from  the  narrow 
zone  than  from  the  wide  zone.  It  will  be  readily  under- 
stood that,  since  the  inflection  of  the  calorific  rays  is  14".7, 
the  first-mentioned  actinometer  receives  radiant  heat  from 
14".7  +  49".6  =  64".3  ;  while  the  actinometer  exposed  to  the 
radiation  from  the  wide  zone  receives  heat  from  1'  42"  +  14".7 
=  116".7.      Consequently,   the  radiant   heat  emanating  from 

64"  3 

the  narrow  zone  will  be  -—  —  0.551  of  that  transmitted 

116".7 

from  the  wide  zone,  hence  somewhat  more  than  one-half. 
Our  investigation  therefore  proves  that  the  radiant  heat 
transmitted  from  the  narrow  border  zone  represented  in 
Fig.  12  is  0.660  -  0.551  =  0.109  more  intense  than  that 
transmitted  from  the  zone  represented  in  Fig.  13,  although 
the  mean  distance  of  the  latter  is  twice  as  far  from  the 
border  of  tbe  photosphere  as  the  mean  distance  of  the  for- 
mer. The  singular  fact  thus  revealed  can  only  be  accounted 
for  by  supposing  that  internal  radiation  is  not  incompatible 
-^^-ith  the  constitution  of  the  photosphere,  and  by  adopting 
Lockyer's  views  expressed  in  the  Senate  House  at  Cambridge, 
1871,  that  "the  photosphere  must  be  a  something  suspended 
in  the  solar  atmosphere."  Let  a  h,  Fig.  14,  represent  a  sec- 
tion of  the  "  suspended "  photosphere,  and  d  c,  g  f,  I'ays  pro- 


CIIAP.  VI.  UNEQUAL  RADIATION  OF  SOLAR  DISC.  129 

jected  towards  the  eartli.  Agreeably  to  the  cuiulitious  men- 
tioned, and  in  view  of  the  fact  that  the  force  of  radiation  from 
incandescent  gases  presenting  equal  areas  varies  nearly  as 
their  depth,  we  are  Avarranted  in  concluding  that,  since  the 
depth  (I  d'  is  greater  than  g  g',  the  radiant  heat  transmitted 
from  the  photosphere  by  the  ray  d  c  Avill  be  greater  than 
that  transmitted  by  the  ray  g  f.  It  should  be  observed  that 
the  energy  transmitted  towards  the  earth  by  d  c  suffers  a 
greater  diminution  than  the  energy  transmitted  by  g  f,  in 
consequence  of  the  greater  depth  of  the  solar  atmosphere 
penetrated.     Hence  the  augmented  energy  estal)lished  by  our 


investigation  does  not  show  the  full  amount  of  the  increase 
of  radiant  heat  transmitted  from  the  border  of  the  sun. 

Having  thus  briefly  stated  the  result  of  my  observations, 
it  \n\\  be  proper  to  mention  that,  before  undertaking  a  sys- 
tematic investigation  of  the  difference  of  theraial  energy  trans- 
mitted to  the  earth  by  radiation  from  different  parts  of  the 
solar  sui-face,  I  examined  thoroughly  the  merits  of  Laplace's 
famous  demonstration  relating  to  the  absorptive  power  of  the 
sun's  atmosphere,  proving  that  only  t^  of  the  energy  deve- 
loped by  the  sun  is  transmitted  to  the  earth.  The  demon- 
stration being  based  on  the  assumption  that  the  sun's  rays 


130 


BABIANT  HEAT. 


emit  energy  of  eqiial  intensity  in  all  directions,  my  iuitiary 
step  was  tLat  of  testing  practically  the  trutli  of  that  propo- 
sition. It  lias  been  asserted  that  Laplace  did  not  propound 
the  singular  doctrine  involved  in  such  a  proposition ;  I 
therefore  feel  called  upon,  before  proving  its  unsoundness, 
to  quote  the  words  employed  by  the  celebrated  mathemati- 
cian (see  "  M^canique  Celeste,"  Tom.  IV.  page  284).  Having 
called  attention  to  the  fact   that   any   portion   of  the   solar 


disc,  as  it  approaches  the  limb,  ought  to  appear  more  bril- 
liant because  it  is  viewed  under  a  less  angle,  Laplace  adds  : 
"  Car  il  est  naturel  de  penser  que  chaque  point  de  la  sur- 
face du  soleil  renvoie  une  lumiere  ^gale  dans  tous  les  sens." 
Let  a  h  c  d  in  the  above  diagram.  Fig.  18,  represent  pai-t  of 
the  border  of  the  sun,  and  h  «,  c  d,  small  equal  arcs ;  a  a', 
h  I)',  c  c',  d  d',  being  parallel  rays  projected  towards  the  earth. 
Laplace's  theory  asserts  that,  owing  to  the  concentration  of 
the  rays,  the  radiation  emanating  from  the  portion  d  c  trans- 
mits greatei'  intensity  towards  the  earth  than  h  a,  in  the  pro- 


CHAP.  VI.  UNEQUAL  RADIATION  OF  SOLAR  DISC.  131 

poilion  oi  c  d  io  f  c.  The  proposition  is  thus  stated  in 
"  Mecanique  Celeste " :  "  Call  d  the  arc  of  a  great  circle  of 
the  sun's  surface,  included  between  the  luminous  point  and 
the  centi'e  of  the  sun's  disc,  the  sun's  radius  being  taken  fur 
unity ;  a  very  small  poi-tiou,  a,  of  the  surface  being  removed 
to  the  distance  6  from  the  centre  of  the  disc,  will  appear  to 
be  reduced  to  the  space  a  cos.  d;  the  intensity  of  its  light 
must  therefore  be  increased  in  the  ratio  of  unity  to  cos.  0." 

In  order  to  disprove  the  correctness  of  the  stated  demon- 
stration, I  have  measui-ed  the  relative  thermal  energy  of  rays 
projected  in  different  directions  from  an  incandescent  metallic 
disc  by  the  method  minutely  described  in  Chap.  XL  The 
follo\ving  brief  description  will,  however,  be  necessary  in  this 
place,  reference  being  had  to  the  illustration  adverted  to 
in  the  said  Chapter  XI.  (see  Plate  21).  Fig.  2  represents  a 
section  of  a  conical  vessel  covered  by  a  movable  semi-spherical 
top,  the  vessel  being  siirrounded  by  a  jacket  through  which 
water  may  be  circulated.  A  revolving  disc  a  a,  composed 
of  cast  iron,  the  back  being  semi-spherical  and  protected  l)y 
fire-clay,  is  suspended  across  the  top  of  the  conical  vessel, 
supported  by  horizontal  journals  attached  at  opposite  sides. 
The  angular  position  of  the  disc  is  regulated  by  a  radial 
handle  b,  connected  to  one  of  the  journals,  the  exact  incli- 
nation to  the  vertical  line  being  ascertained  by  means  of  a 
graduated  quadrant  d.  An  instrument  c,  capable  of  indicat- 
ing the  intensity  of  the  radiant  heat  transmitted  by  the  incan- 
descent disc,  is  applied  at  the  bottom  of  the  conical  vessel. 
The  movable  cover  and  its  lining  of  fire-clay  being  removed, 


132  BADIANT  HEAT.  CHAP.  vi. 

the  cast-iron  disc  is  lieated  in  an  air-furnace  to  a  tempera- 
ture of  1,800°  F.  It  is  then  removed  by  appropriate  tongs, 
and  susj)ended  over  the  conical  vessel,  the  lining  and  cover 
being  quickly  replaced.  The  temperature  shown  by  the  instru- 
ment at  the  bottom  of  the  conical  vessel,  resulting  from  the 
action  of  the  radiant  heat  of  the  disc,  is  then  recorded  for 
every  tenth  degree  of  inclination.  The  investigation,  it  may 
be  briefly  stated,  shows  that  the  temperature  imparted  by 
radiation  to  the  recording  instrument  is  exactly  as  the  sines 
of  the  angles  of  inclination  of  the  disc.  Hence,  at  an  incli- 
nation of  10  deg.  to  the  vertical  line,  the  temperature  imparted 
to  the  thermometer  is  scarcely  i  of  that  imparted  when  the 
disc  faces  the  thermometer  at  right  angles  ;  yet  in  both  cases 
an  equal  amount  of  surface  of  an  equal  degree  of  incandes- 
cence is  radiating  towards  the  instrument.  Laplace  and  his 
followers  have  evidently  overlooked  this  important  and  some- 
what anomalous  fact  proving  that  radiation  emanating  from 
heated  bodies  is  incapable  of  exerting  full  energy  in  more 
than  one  direction.  Our  practical  experiments  -ttath  the 
revolving  incandescent  disc  have  thus  fully  demonstrated 
the  truth  of  the  proposition  intended  to  be  established — 
namely,  that  the  rays  emanating  from  incandescent  planes 
do  not  transmit  heat  of  equal  intensity  in  all  directions,  the 
energy  transmitted  being,  as  stated,  proportionate  to  the  sines 
of  their  angle  of  inclination  to  the  radiating  surface. 

The  next  step  in  the  preliminary  investigation  was  that 
of  measuring  the  radiant  energy  transmitted  in  a  given  direc- 
tion by  an  incandescent  solid  metallic  sphere.     For  this  pur- 


CHAP.  Ti.  USEQUAL  RADIATION  OF  SOLAR  DISC.  133 

pose  I  employed  a  double  conical  vessel  similar  to  the  one 
already  described,  the  incandescent  sphere  being  suspended 
over  the  conical  vessel  in  the  manner  minutely  described  in 
Chap.  XII.  A  brief  explanation  will,  however,  be  necessary 
here,  reference  being  had  to  the  diagram  on  Plate  24,  repre- 
senting four  spheres.  Figs.  3,  4,  5,  and  G.  Each  sphere  is  divided 
into  four  zones,  A,  B,  C,  and  D,  occupying  unequal  arcs,  but 
containing  equal  convex  areas.  Semi-spherical  screens,  com- 
posed of  non-conducting  substances,  were  ajiplied  below  each 
sphere,  provided  with  annular  openings  arranged  as  shown 
in  the  diagram.  Through  these  annular  openings  the  radiant 
heat  from  the  incandescent  zones  D,  C,  B,  and  A  was  trans- 
mitted to  the  thermometers  /,  g,  Ji,  and  k  respectively.  Pere 
Secchi  and  other  followers  of  Laplace  will  be  siirprised  to 
learn  that  when  the  suspended  sphere  was  maintained  at  a 
temperature  of  1,800°  R,  the  radiation  fi-om  the  zone  C,  Fig. 
4,  imparted  a  temperature  of  27°.49  F.  to  the  thermometer 
g ;  while  the  radiation  from  the  zone  A,  Fig.  6,  imparted 
only  6°.19  F.  to  the  thermometer  l\  Let  iis  bear  in  luind 
that  the  radiating  surface  I  m  oi  the  zone  A  is  equal  to  the 
radiating  surface  p  q  oi  the  zone  C.  The  stated  great  dif- 
ference of  temperature  produced  by  the  radiation  from  zones 
of  equal  area  funiishes  additional  proof  that  Laplace  based 
his  remarkable  analysis  on  false  premises.  "  The  sun's  disc 
ought  to  appear  more  brilliant  towards  the  border  because 
viewed  imder  a  less  angle,"  we  are  told  by  the  great  analyst. 
The  instituted  pi-actical  tests,  however,  prove  positivel}-  that 
the  energy  of  the  rays  projected  from  the  border  of  an  incan- 


134  BADIAWI EEAT.  chap.  vi. 

descent  sphere  is  greatly  diminished  because  viewed  under  a 
less  angle  from  the  point  occupied  by  the  recording  thermo- 
meter. 

The  result  of  the  experiment  with  the  revolving  incan- 
descent disc  shows  that  if  the  small  arc  h  a,  in  Fig.  18,  be 
reduced  until  the  field  represented  by  h'  a'  becomes  equal 
to  the  field  represented  by  c'  d',  the  radiant  energy  trans- 
mitted through  each  of  those  fields  will  be  alike ;  the  reason 
being  that  the  number  of  rays  of  diminished  intensity  passing 
through  c'  d'  will  be  as  much  greater  than  the  number  of 
rays  of  maximum  intensity  passing  through  h'  a'  as  c  d  is 
greater  than  the  reduced  h  a  —  f  c.  It  should  be  observed 
that  c  6?  is  so  small  that  we  may,  without  appreciable  error, 
regard  it  as  a  straight  line,  and  /  c  as  the  sine  of  the  angle 
c  d  f.  It  follows  from  this  demonstration  that  if  the  solar 
atmosphere  exerted  no  retarding  influence,  the  radiant  heat 
transmitted  towards  the  earth  would  be  alike  for  equal  areas 
of  the  solar  disc ;  more  correctly,  for  areas  subtending  equal 
angles,  since  the  receding  part  of  the  solar  sui-face  is  at  a 
greater  distance  from  the  earth  than  the  central  part. 

Encouraged  by  the  results  of  the  instituted  practical  tests 
showing  the  actual  intensity  transmitted  by  radiant  heat  ema- 
nating from  incandescent  spheres  and  inclined  discs,  I  devised 
the  method  before  described,  proving  positively  that  the  polar 
and  equatorial  regions  of  the  solar  disc  transmit  radiant  heat 
of  equal  intensity  to  the  earth,  and  that  the  sun  emits  heat 
of  equal  energy  in  all  directions.  Accepting  Secchi's  doctrine 
relating  to  the  retardation  suffered  by  calorific  rays  in  passing 


CHAP.  VI.  UNEQUAL  RABIATIOX  OF  SOLAR  DISO.  135 

through  atmospheres — namely,  that  the  diminution  of  energy 
is  as  the  depth  penetrated  b}-  the  rays — I  liave  showii,  by  the 
easy  calcuhxtion  before  presented,  that  the  absorption  by  the 
sohir  atmosphere  cannot  exceed  Vo*uV  of  the  radiant  energy 
emanating  from  the  photosphere. 

Concerning  the  plan  resorted  to  by  the  Director  of  the 
Roman  Observatory  and  others  of  investigating  the  sun's 
image  instead  of  adopting  the  method  of  direct  observations, 
I  will  merely  observe,  in  addition  to  what  has  already  been 
stated,  that  the  information  contained  in  the  several  works 
of  the  Roman  astronomer  furnishes  the  best  possible  guide 
in  judging  of  the  efficacy  of  image-investigation.  Let  us  select 
his  account  of  the  investigations  conducted  between  the  19th 
and  23d  of  March,  1852.  Having  pointed  out  that  in  these 
experiments  it  was  impossible  to  approach  within  a  minute 
of  the  edge  of  the  sun,  and  that  during  a  later  observation 
— date  not  mentioned — he  had  approached  ^vithin  a  minute, 
the  investigator  obseives :  "  But  at  this  extreme  limit,  even 
making  use  of  the  most  accurate  means  of  observation,  we 
find  difficulties  Avhicli  it  is  impossible  to  overcome  com- 
pletel)'."  In  addition  to  this  emphatic  expression  regarding 
the  difficulties  encountered,  the  author  adds  :  "  Moreover,  it 
is  impossible  to  study  the  edge  alone,  for  the  unavoidable 
motions  of  the  image  do  not  admit  of  its  being  retained  at 
exactly  the  same  point  of  the  pile ;  we  have,  therefore,  been 
unable  to  push  the  exactness  as  far  as  we  hoped,  and  we 
have  discontinued  the  pursuit  of  these  researches,  although 
the  results  obtained  are  quite  interesting."     (See  revised  edi- 


136  BABIANT  HEAT.  CHAP.  vi. 

tion  of  "  Le  Soleil,"  Vol.  I.  p.  205.)  It  is  needless  to  iustitute 
a  comparisou  between  a  system  of  Avhicli  its  founder  speaks 
so  despondiugly  and  one  wliicli  enables  us  to  push  our  inves- 
tigations to  the  extreme  limit  of  the  solar  disc,  admitting 
of  entire  zones  being  viewed  at  once,  instead  of  only  small, 
isolated  spots. 

The  foregoing  demonstration,  showing  that  the  solar  atmo- 
sphere absorbs  0.144  of  the  heat  radiated,  it  should  be  remem- 
bered, is  based  on  the  assumption  that  the  retardation  is  as 
the  depth  penetrated  by  the  rays.  In  view  of  the  fact  that 
projectile  force  diminishes  inversely  as  the  square  of  the 
depth  of  the  medium  penetrated,  we  are,  of  course,  not  com- 
pelled to  accept  the  stated  assumption.  Adopting  the  dyna- 
mical law  relating  to  projectile  motion,  referred  to,  it  will 
be  found  that  the  retardation,  instead  of  being  0.144,  will  be 
(3  55i-'oo3ii)^  ~  0.057.  But  even  this  apparently  small  amount 
of  absorption  of  the  radiant  intensity  cannot  be  satisfactorily 
accounted  for,  since  the  mechanical  energy  developed  by  the 
sun  is  at  least  322,000  thermal  units  per  minute  upon  an  area 
of  one  square  foot.  Consequently,  322,000  X  0.057  X  772  = 
14,169,288  foot-pounds  represent  the  mechanical  equivalent  of 
tU-o  of  the  radiant  energy  emanating  from  each  square  foot  of 
the  photosphere.  Owing  to  the  high  temperature  and  conse- 
quent lightness,  no  conceivable  work  performed  within  the 
solar  atmosphere  can  satisfactorily  account  for  the  disappear- 
ance, every  minute,  of  such  an  amount  of  energy.  It  is  there- 
fore demonstrable  that  we  have  not  underrated  the  absorptive 
power. 


CHAPTER  VII. 


THE  SOURCE  OF  SOLAR  ENERGY. 


Sir  AVilliaji  Thomson,  iu  his  celebrated  paper  on  the 
Mechanical  Energies  of  the  Solar  System,  read  before  the 
Royal  Society  of  Edinburgh,  April,  1854,  puts  the  question  : 
"AVhat  is  the  soiu'ce  of  mechanical  eueigy,  drawn  upon  Ijy 
the  sun,  in  emitting  heat,  to  be  dissipated  in  space  ? "  Having 
very  briefly  examined  the  question,  he  adds  :  "  We  see,  then, 
that  all  theories  which  have  yet  been  proposed,  as  well  as 
every  conceivable  theory,  must  be  one  or  other,  or  a  combi- 
nation, of  the  following  three:  (1)  That  the  sun  is  a  heated 
body  losing  heat.  (2)  That  the  heat  emitted  from  the  sun 
is  due  to  clieniical  action  among  materials  originally  belong- 
ing to  the  mass,  or  that  the  sun  is  a  great  fire.  (3)  That 
meteoi-s  falling  into  the  sun  give  rise  to  the  heat  which  he 
emits."  The  second  and  third  of  these  suppositions  having 
been  disposed  of  l)y  more  recent  investigations,  let  us  con- 
fine our  discussion  to  the  first  hypothesis,  that  the  sun  is  a 
heated  body  losing  heat,  regarding  which  the  eminent  phy- 
sicist remarks:  "In  alluding  to  theories  of  solar  heat  in  a 
foiTuer   communication  to  the  Ro\al    Society   I   pointed  out 

137 


138  BADIANT  HEAT.  chap.  vii. 

tliat  the  first  hypothesis  is  quite  untenable.  In  fact,  it  is 
ueuionstrable  that,  unless  the  sun  be  of  matter  inconceivably 
more  conductive  for  heat,  and  less  volatile,  than  any  terres- 
trial meteoric  matter  we  knoAV,  he  would  become  dark  in 
two  or  tliree  minutes,  or  days,  or  months,  or  years,  at  his 
present  rate  of  emission,  if  he  had  no  source  of  energy  to 
draw  from  but  primitive  heat.  This  assertion  is  founded  on 
the  supposition  that  conduction  is  the  only  means  by  which 
heat  could  reach  the  sun's  surface  from  the  interior,  and 
perhaps  recpiires  limitation.  For  it  might  be  supposed  that, 
as  the  sun  is  no  doubt  a  melted  mass,  the  brightness  of  his 
surface  is  constantly  refreshed  by  incandescent  fluid  rushing 
from  below  to  take  the  place  of  matter  falling  upon  the 
surface  after  becoming  somewhat  cooled  and  consequently 
denser — a  process  which  might  go  on  for  many  years  with- 
out any  sensible  loss  of  brightness.  If  we  consider,  however, 
the  whole  annular  emission  at  the  present  actual  rate,  we 
find,  even  if  the  sun's  thermal  capacity  were  as  great  as 
that  of  an  equal  mass  of  water,  that  his  mean  temperature 
would  be  lowered  by  about  3°  Cent,  in  two  years."  It  -would 
appear  from  this  reasoning  that  Sir  William  Thomson  had 
overlooked  Laplace's  important  nebular  theory  which  leads 
to  the  conclusion  that  the  sun's  heat  is  the  result  of  con- 
densation caused  by  gravitation.  Obviously  this  condensa- 
tion is  progressing  at  the  present  time  as  fast  as  the  mass 
cools,  the  process  being  the  same  now  as  millions  of  years  ago, 
the  heat  generated  by  the  condensation  becoming  gradually 
intensified  in  the  inverse  ratio  of  the  radius  of  the  contract- 


CHAP.  VII.  Till-:  aorucK  of  holai;  enei;gy.  inn 

ing  mass.  Let  us  consider,  liowever,  that  the  matter  com- 
posing this  contracting  mass  siitfei-s  a  proportionate  reduction 
of  velocity ;  hence  the  emission  of  heat  becomes  constant 
for  a  given  area  of  the  soLir  suiface,  notwithstanding  the 
augmentation  of  intensity.  But,  wliile  the  emission  from  a 
given  area  is  constant,  the  bulk  of  the  cooling  mass  is  con- 
tinually diminishing.  The  important  consequences  of  this 
diminution  of  bulk  will  l^e  otnisidered  presently.  Of  course 
it  will  not  be  necessary  to  prove  that  the  sun  is  continu- 
ally becoming  smaller,  since  all  incandescent  bodies  shrink 
rapidly  if  permitted  to  radiate  freely,  the  rate  being  nearly 
proportional  to  the  degree  of  incandescence.  Our  task,  there- 
fore, will  be  confined  to  a  simple  demonstration  showing 
that  the  emission  of  322,000  thermal  units  per  minute  on 
each  squai-e  foot  of  solar  surface,  established  in  Chaj)ter  V., 
is  capable  of  being  developed  by  the  contraction  of  the  mass, 
in  accordance  "with  the  nebular  theory  of  Laplace.  At  first 
sight  it  would  appear  that  no  probable  amount  of  contrac- 
tion of  the  solar  mass  could  develop,  by  gravitation  towards 
the  centre,  an  amount  of  mechanical  energy  of  322,000  X 
772  =  248,584,000  foot-pounds  per  minvte  for  each  square 
foot  of  the  surface  of  the  sun.  Yet  so  A-ast  is  the  amount 
of  matter  covered  by  the  insignificant  area  of  144  square 
inches  of  the  solar  surface — in  other  words,  such  is  the  con- 
tents of  a  spherical  pyramid  the  base  of  which  is  one  square 
foot,  and  whose  length  is  equal  to  the  sun's  radius — that  a 
veiy  small  amount  of  contraction  suffices  to  develop,  l>y  gra- 
vitation towards  the  solar  centre,  the  stated  enormous  mecha- 


140  BADIANT  HEAT.  chap.  vii. 

uical  enei'gy.  It  will  be  readily  understood  that  the  energy 
developed  by  the  shrinking  of  a  spherical  pyramid  whose  sides 
are  sectors  of  the  great  circle  of  the  sun  M'ill  represent  cor- 
rectly the  relative  energy  produced  by  the  shrinking  of  the 
entire  solar  mass.  Hence,  if  Ave  can  determine  the  amount 
of  longitudinal  contraction  of  the  supposed  spherical  pyramid 
requisite  to  produce,  by  gravitation  tow^ai'ds  the  centre  of  the 
mass,  a  mechanical  energy  of  248,584,000  foot-pounds  per 
minute,  we  need  not  enter  into  any  further  computation,  since 
a  corresponding  contraction  of  the  sun's  radius  will  develop 
for  every  sqxiare  foot  of  his  surface  a  like  energy. 

Let  I  K  S,  Fig.  1  (see  Plate  14),  represent  the  great 
circle  of  the  sun,  a  m  a'  the  spherical  pyramid  referred  to, 
and  Fig.  2  the  said  pyramid  drawn  to  a  larger  scale,  its  axis 
being  divided  into  ten  equal  parts.  It  is  proposed  to  ascer- 
tain what  extent  of  longitudinal  contraction  of  the  spherical 
pyramid  a  m  a'  is  necessary  to  produce  an  amount  of  djaiamic 
energy  corresponding  with  that  developed  by  the  radiation 
from  1  sq.  ft.  of  the  solar  surface  in  a  given  time.  The  in- 
vestigation will  be  facilitated  and  more  readily  comprehended 
if  we  compute  the  amount  of  energy  developed  by  a  definite 
contraction  of  the  sun's  radius,  say  one  foot.  Let  us,  there- 
fore, suppose  that  the  surface  a  a',  the  distance  of  which  is 

'- X  5,280  =  2,250,821,760  ft.  from  m,  has  fallen  through 

a  space  of  one  foot,  the  intermediate  points  b,  c,  d,  etc.,  par- 
ticipating proportiouably  in  the  fall.  Assuming  that  the  solar 
mass  remains  homogeneous  during  the  contraction,  it  follows 


CHAP.  Til.  THE  SOURCE  OF  SOLAU  EXERGT.  141 

from  Newton's  demonstration  ("  Principia,"  Lib.  I.  Prop. 
LXXIII.)  that,  since  a  particle  just  within  the  circumference 
of  the  sphere  at  a  is  ten  times  further  from  the  centre  m 
than  a  partick-  at  /,  the  foniicr  will  be  attracted  towards  ni 
with  ten  times  greater  force  than  the  latter.  It  will  be  per- 
ceived, on  reflection,  that,  for  a  given  movement  towards  the 
centre,  the  quantity  of  matter  put  in  motion  at  a  will  be 
greater  than  at  J,  in  the  ratio  of  the  squares  of  a  a',  and  / 
1,  or  100  ;  1.  Hence,  in  accordance  with  the  demonstration 
referred  to,  a  given  radial  depth  of  the  solar  mass  at  a  will 
exert  a  force  towards  w  10  X  100  =  1,000  times  greater  than 
an  equal  radial  depth  at  I.  But  in  computing  the  dynamic 
energy  developed  by  the  shrinking  of  the  sun,  it  must  be 
borne  in  mind  that  a  particle  at  a  falls  through  a  distance 
ten  times  greater  than  a  particle  at  I.  The  length  of  the 
onlinates  of  the  curve  j)  (,  Fig.  3,  representing  the  ratio  of 
dynamic  energy  developed  at  the  respective  distances  from 
the  sun's  centre,  has  been  calculated  accordinglj'.  A  cui-sory 
examination  of  Fig.  2  can  scarcely  fail  to  lead  to  the  suppo- 
sition that  the  mass  composing  the  smaller  sections  of  the 
sjiherical  i)}ramid  near  the  centre  of  the  sphere  Avill  be 
attracted  by  the  larger  mass  composing  the  sections  near 
the  circumference.  Newton  has  disposed  of  this  question 
by  a  geometrical  demonstration  which,  considering  the  foiiii 
t)f  the  attracting  mass,  and  the  e.xtreme  complication  arising 
from  the  varying  direction  and  unequal  magnitude  of  the 
attracting  forces,  may  be  I'egarded  as  one  of  the  most  ele- 
gant of  his  masteily  demonstrations  of  inqxirtant -propositions 


143  RADTANT  HEAT.  chap.  Tii. 

and  tlieorems.  Unless  it  can  be  proxed  that  a  jiarticle  at  P 
is  not  attracted  by  any  portion  of  the  mass  contained  within 
the  external  spherical  superficies  IKS  and  the  interior  sphe- 
rical superficies  P  j^,  we  must  assume  that  the  mass  compos- 
ing the  sections  near  the  base  of  the  spherical  pyramid  will 
exert  the  disturbing  attraction  before  alluded  to.  Hence 
our  demonstration  of  the  enei'gy  produced  by  the  attraction 
of  the  matter  within  the  sun,  during  shrinking,  falls  to  the 
ground  unless  it  can  be  shown  that  every  particle  compos- 
ing the  spherical  pyramid  is  in  perfect  repose  as  regards  the 
attraction  exerted  by  exterior  particles.  The  great  geometer 
thus  establishes  that  repose  :  "  Let  II  I  K  L  be  a  spherical 
superficies  and  P  a  corpuscle  placed  -within.  Through  P  let 
there  be  drawn  to  this  superficies  the  t\vo  lines  II  K,  I  L, 
intersecting  very  small  arcs  II  I,  K  L ;  and  because  the  tri- 
angles H  P  I,  L  P  K  are  homogeneous,  those  arcs  will  be 
proportional  to  the  distances  H  P,  L  P,  and  any  particles 
at  H  I  and  K  L  of  the  spherical  superficies,  terminated  by 
right  lines  passing  through  P,  will  be  in  duplicate  ratio  of 
those  distances.  Therefore  the  forces  of  these  particles  ex- 
erted upon  the  body  P  are  equal  between  themselves.  For 
the  forces  are  as  the  particles  directly,  and  the  squares  of  the 
distances  inversely.  And  these  two  ratios  compose  the  ratio 
of  ecpiality.  The  attractions,  therefore,  being  made  equally 
towards  contrary  parts,  destroy  each  other ;  and,  by  a  like  rea- 
soning, all  the  attractions  through  the  whole  spherical  super- 
ficies are  destroyed  by  contrary  attractions.  Therefore  the 
body  P  will  not  be  any  way  impelled  by  those  attractions." 


cUAi>.  VII.  THE  SOVUCE  OF  SOLAU  ESEEGY.  Ul! 

Sir  Isaac  Newton,  iu  his  demoustratious  relatiug  to  sphe- 
rical bodies,  supposed  these  to  be  composed  of  an  infinite 
number  of  spherical  superficies,  the  thickness  of  which  he 
thus  defines:  "By  the  superficies  of  whlcli  I  here  imagine 
the  solids  composed,  I  do  not  mean  superficies  purely  mathe- 
matical, but  orbs  so  extremely  thin  that  their  thickness  is  as 
nothing ;  that  is,  the  evanescent  orbs  of  which  the  sphere  will 
at  last  consist  when  the  number  of  the  orbs  is  increased,  and 
their  thickness  diminished  without  end." 

Referring  to  Fig.  3,  it  should  be  p;irticularly  observed 
that  the  ordinates  of  the  curve  2)  t  do  not  indicate  the  force 
exerted  by  mere  attraction.  As  already  stated,  their  length 
represeuts  the  dynamic  energy  developed  at  the  indicated 
distances  from  the  solar  centre.  Consequently,  the  energy 
actually  developed  by  the  shrinking  of  the  mass  is  repre- 
sented by  the  superficies  o  p  t,  while  the  rectangle  o  p  u  t 
represents  the  energy  that  would  be  called  forth  if  the  force 
exei-ted  at  every  point  of  the  axis  of  the  spherical  pyramid 
were  the  same  as  that  exerted  at  a  a'.  Having  already  pointed 
out  the  manner  of  determining  the  length  of  the  ordinates  of 
the  curve  p>  t,  it  will  suffice  to  state  that  their  mean  length 
is  0.20015  oi  0  p  ;  hence  the  superficies  o  p  t  \&  0,20015  of 
the  superficies  o  p  u  t. 

Let  us  no^v  consider  whether  the  want  of  homogeneity 
of  the  solar  mass  will  materially  affect  the  calculated  amount 
of  energy  developed  by  the  gravitating  force  during  the  sun's 
shrinking.  Referring  to  the  diagram  Fig.  3,  it  will  be  seen 
that  the  energy  exerted  by  a  given  small  amount  of  contj-actiou 


144  EADIANT  MEAT.  chap.  vii. 

at  a  section  equidi.stant  between  ni  and  a — viz.,  at  /'  5 — will 

625 
be,  as  shown  by  the  length  of  the  ordinates,  =  iV  of 

that  exerted  by  a  like  amount  of  contraction  at  a  a' ;  and 
that,  since  m  f  is  one-half  of  m  a,  the  energy  developed  by 
the  contraction  of  the  mass  contained  within  the  spherical 
pyramid  /  in  5  amounts  to  only  -h  of  that  developed  by  the 
contraction  of  the  mass  contained  in  the  spherical  pyramid 
a  m  a'.  Now,  the  volume  of  the  spherical  pyramid  /  m  5 
represents  that  of  a  sphere  the  diameter  of  which  is  one-half 
of  the  sun,  while  the  spherical  pyramid  (/  m  a'  represents 
the  volume  of  the  entire  solar  mass.  The  energy  resulting 
from  gravitation  during  the  contraction  of  the  central  sphe- 
rical mass  P  p  being  thus  only  ^V  of  the  energy  resulting 
from  gravitation  during  the  contraction  of  the  spherical  mass 
I  K  S,  it  will  be  perceived  that  the  degree  of  density  of  the 
matter  near  the  sun's  centre  will  not  materially  affect  the 
result  of  our  calculations  founded  on  j^ei'fect  homogeneity. 

We  may  now  proceed  to  ascertain  the  amount  of  dynamic 
energy  produced  by  the  assumed  contraction  of  one  foot  of 
the  axis  of  the  sj^herical  pyramid  a  m  a'.  Having  already 
demonstrated  that  the  said  energy  will  be  0.20015  of  that 
produced  by  the  gravitation  of  a  homogeneous  mass,  the  sec- 
tion of  which  is  one  square  foot,  extending  from  a  a'  to  m, 
it  only  remains  to  determine  the  weight  of  one  cubic  foot  at 
the  surface  of  the  siin.  The  weight  of  the  solar  mass  being 
85.6  lbs.  per  cubic  foot,  while  the  sun's  attraction  is  27.2  times 
greater  than  terrestrial  attraction,  the   weight   of  one  cubic 


cuAP.  VII.  TUi:  sorncE  of  solar  EXEHOY.  145 

foot  of  the  solar  sui-face  will  be  27.2  X  85.()  =  2,328.3  lbs. ; 
multipl}nng  this  weight  by  the  sun's  radius,  expressed  in  feet, 
we  have  2,328.3  X  2,250,821,000  =  5,240,586,000,000,  which 
product  nniltiplit'd  by  0.20015  shows  that  the  gravitating 
energy  of  the  matter  contained  in  the  spherical  pyramid,  ex- 
erted during  a  longitudinal  contraction  of  one  foot,  amounts 
to  1,048,900,000,000  foot-pounds.  Dividing  this  latter  product 
by  the  ascertained  solar  emission  of  248,584,000  foot-pounds 
per  minute,  it  will  be  seen  that  the  mechanical  energy  pro- 
duced by  the  shrinking  of  one  foot  of  the  sun's  radius  is  suf- 
ficient to  make  good  the  power  lost  by  solar  emission  during 
a  period  of  4,219.5  minutes.  If  we  then  divide-  this  quutieiit 
in  the  minutes  in  a  year,  525,960,  it  will  be  found  that  a  fall 
of  124.65  feet  of  the  solar  surface  per  annum  must  take  place 
in  order  to  sustain  the  present  emission  of  heat.  At  this  rate 
of  shrinking  the  diameter  of  the  sun  will  be  reduced  Tshm  in 
the  coui-se  of  1,805  years.  It  has  already  l)een  observed  that 
the  intensity  of  the  radiant  heat  will  not  diminish  with  the 
diminished  size  of  the  sun.  On  the  contraiy,  for  a  given 
area  of  the  solar  surtace,  the  dynamic  energy  produced  by 
a  triven  rate  of  shrinking  will  be  increased,  since  the  ma.ss 
remains  the  same,  while  the  attraction  is  invei-sely  propor- 
tional to  the  distance  from  the  centre.  Rut  the  rate  will 
diminish  w  ith  the  contraction  of  the  sphere  ;  hence  a  shrink- 
ing of  f'oth  of  the  sun's  diameter,  instead  of  occupying  1,000 
X  1,805  =  1,805,000  yeai-s,  will  require  somewhat  more  than 
2,000,000  yeai-s.  At  the  end  of  that  period  the  gravitating 
energy  will   continue   to  develop,   as  at  present,  an    amount 


146  EADIANT  HEAT.  chap.  vii. 

of  dynamic  energy  i-epresented  by  322,000  tLennal  units  per 

niiunte  for  eacli   supeificial  foot ;    but  tLe  radiating  sm-face 

— i.e.,  the  area  of   tlie  solar   disc — will   liave    diminished  in 

the  ratio  of  nearly  10'  to  9". 

The    present    maxinuim    temperature    produced    by    solar 

radiation  on  the  ecliptic  when  the  earth  is  in  aphelion  being 

67.2  deg.  (see  Chap.  III.),  while  the  intensity  of  radiant  heat 

diminishes  as  the  area  of  the  radiating  surface,  it  follows  that 

at  the  end  of  2,000,000  years  from  the  present  time  the  tro- 

9"  X  67  2 
pical  solar  intensity  Avill  be  reduced  to  — =  54.4  deg. 

Falirenheit.  The  result  of  the  elaborate  investigations  of  solar 
intensity  described  in  the  preceding  chapter  proves  the  cor- 
rectness of  the  foregoing  calculations  based  on  the  a^'ea  of  the 
solar  disc,  and  disposes  of  the  opinion  held  by  some  physi- 
cists that  thei'e  is  no  established  relation  between  the  dia- 
meter of  the  sun  and  the  transmitted  energy.  It  was  found, 
during  the  investigation  referred  to,  that,  in  shutting  out  the 
radiation  from  the  external  zones  of  the  sun  and  exposing 
an  actinometer  to  the  I'ays  emanating  from  a  circular  ai'ea  at 
the  centre  measuring  380,000  miles  in  diameter,  the  intensity 
of  the  radiant  heat  was  reduced  to  one-third  of  that  trans- 
mitted to  another  actinometer  exposed  to  the  radiation  from 
the  entire  solar  disc.  Can  we  douT)t,  tlieu,  that  the  future 
diminution  of  the  diameter  of  the  sun  will  cause  a  corre- 
sponding diminution  of  the  transmitted  energy  ?  Adopting 
the  same  mode  of  calculating  the  solar  intensity  for  past  ages 
as  the  foregoing  calculation  of  future  solar  intensity,  it  will 


CHAP.  VII.  THE  SOURCE  OF  SOLAR  ESEIiGY.  147 

1)6  tV)mul  tliat  the  teiii])erature  proiluced  Ijy  sular  radiation 
:?,000,000  years  ago  (owing  to  tbe  greater  diameter  of  the  sun 

.      11'  X  67.2 

at  that  period)  must  have  been  nearly  ; =  81  des:. 

I  /  ''10  ° 

l''ali.  within  the  tropics.  Concerning  this^great  intensity  of 
the  radiant  heat,  and  the  consequent  high  atmospheric  tempe- 
rature, we  are  justified  in  assuming  that  increased  evaporation 
of  the  sea,  and  coTTPsponding  humidity  of  the  atmosphere,  mol- 
lified the  apparently  destructive  temperature,  calling  forth  the 
luxuriant  flora  ^\•hich  geology  has  made  us  acquainted  with. 
The  computed  diminution  of  solar  intensity,  67  deg.  —  54  deg. 
=  13  deg.,  during  the  next  2,000,000  years,  will  be  deemed 
extravagant  by  those  who  do  not  bear  in  mind  that  we  must 
base  our  computation  on  the  assumption  that  a  contimiouts 
power  will  be  exerted  during  the  stated  period  capable  of 
developing,  as  at  present,  the  stupendous  energy  of  248  mil- 
lions of  foot-pounds  in  a  single  minute  for  each  square  foot 
of  the  surface  of  a  sphere  whose  diameter  exceeds  850,000 
miles.  Persons  speculating  on  the  cause  of  solar  energy  will 
do  well  to  consider  that  this  inconceivable  amount  of  work 
cannot  be  pei-fonned  with  a  less  expenditure  than  the  motive 
energy  developed  by  the  fall  of  a  mass  equal  to  the  mass 
contained  in  the  sun.  But  a  continiioits  development  of  such 
an  amount  of  energy  is  obviously  impossible,  since  the  dis- 
tance is  limited  through  Avhich  the  mass  can  fall.  Now,  the 
foregoing  demonstration  enables  us  to  determine  the  said  limit 
\ni\\  sufiicient  exactness  to  prove  that,  although  the  efficiency 
of  the  great  motor  during  the  past  may  be  measured  by  lain- 


148  RADIANT  MEAT.  chap.  vii. 

dreds  of  niillious  of  yeurs,  its  future  efficiency  will  be  of  com- 
paratively brief  duration. 

Statements  frequently  made  relating  to  the  permanency  of 
solar  heat,  based  on  the  assertion  that  no  diminution  has  been 
observed  during  historic  times,  have  no  weight  in  view  of  our 
demonstration  showing  that  a  shrinking  of  A  of  the  sun's  dia- 
meter can  only  reduce  the  intensity  from  81  deg.  to  67.2  deg., 
difference  =  13.8  deg.,  in  the  course  of  two  millions  of  years. 
This  period  being  500  times  longer  than  "historic  times,"  it 
will  be  seen  that  the  diminution  of  the  temperature  produced 

13  8 
by  solar  radiation  has  not  exceeded  — rr  =  0.027,  or  tV  deg. 
■'  500 

Fah.,  since  the  erection  of  the  Pyramids. 

It  will  be  proper  to  notice,  before  concluding  our  brief 
investigation  of  the  source  of  solar  energy,  that  the  develop- 
ment of  heat  by  the  shrinking  of  the  sun,  however  fully 
demonstrated,  leaves  the  important  question  unanswered  : 
How  is  the  heat  generated  by  gravitation  within  the  mass 
transmitted  to  the  surface  ?  If  the  matter  within  the  sun 
is  a  perfect  conductor  of  heat — a  very  improbable  supposi- 
tion— that  fact  alone  furnishes  a  satisfactory  answer.  Imper- 
fect conductivity,  on  the  other  hand,  calls  for  other  means 
of  transmitting  the  energy  from  within  to  the  surface.  What 
those  means  'are  presents  a  problem  suscejitible  of  positive 
demonstration.  The  api)lication  of  cold  at  the  surface  of 
any  heated  gaseous  fluid,  or  the  reduction  of  temperature  of 
siich  a  fluid  by  radiation  upwards,  invariably  produces  a  ver- 
tical circulation  within  the  heated  mass,  the  particles  cooled 


CHAP.  VII.  TtlE  auLltVE  OF  HOLAR  ESKViGl'.  149 

ilesceiuliug,  iu  virtue  of  tlieir  incieased  sipecific  gravity.  Evi- 
ileiitly  a  uiimber  i)f  particles  desceudiug  oue  after  the  other 
will  produce  a  downward  vertical  current  of  greater  specific 
gravity  than  the  rest  of  the  fluid.  Now,  as  this  current,  com- 
posed of  comparatively  cold  and  heavy  particles,  descends, 
it  displaces  a  corresponding  bulk  of  heated  fluid,  which,  since 
there  is  no  unoccupied  space  below,  must  rise  to  the  surface. 
Descending  and  ascending  currents  of  nearly  uniform  magni- 
tude and  velocity  will  thus  be  established  in  the  heated  fluid 
mass,  provided  no  disturbing  force  be  applied,  causing  ai;ita- 
tion  either  at  the  suiface  or  within.  It  needs  no  proof  to 
show  that  in  case  disturbing  force  be  applied  the  refularitN 
of  the  distribution  of  descending  and  ascending  currents 
within  the  fluid  ceases,  and  that  the  established  vertical 
circulation,  instead  of  being  alike  at  all  points,  becomes 
divided  into  groups.  Nor  is  it  necessary  that  the  distuib- 
ing  force  should  be  of  great  magnitude.  Obviously  a  con- 
tinued uniform  distribution  of  the  descending  and  ascending' 
currents  through  the  heated  mass  calls  for  perfect  aljsence 
of  disturbing  influences  of  any  kind.  Xow,  within  tlie  sun 
the  descending  and  ascending  masses  of  heated  matter  are 
influenced  by  numerous  disturbing  causes.  (1)  The  particles 
composing  the  descending  currents,  possessing  the  vis  viva 
due  to  the  angular  velocity  of  the  sun's  surface,  gradually 
encounter  the  particles  of  less  angular  velocity  composing 
the  ascending  columns.  Conflicting  motions  will  thus  be 
produced,  resulting  in  an  inci-ea-sed  angular  velocity  of  the 
interior  of  the  solar   mass ;   w  hile   {^2)  the   particles   of   the 


150  EADIANT  HEAT.  chap.  vn. 

asceudiug  cuiTeiitj<,  wliicli  start  witli  a  slow  angular  velo- 
city, will  be  gradually  impelled  by  tlie  surrounding  mass 
during  their  ascent ;  tlie  energy  thereby  absorbed  causing  a 
lagging  of  the  entire  solar  mass  towards  the  surface.  Of 
course  there  is  an  exchange  of  angular  vis  viva  between 
the  descending  and  ascending  currents,  but  obviouslj^  there 
will  be  a  loss,  productive  of  perceptible  lagging  at  the  sur- 
face of  the  rotating  mass.  (3)  The  attraction  of  the  plane- 
tary masses  ^\■ill  seriously  disturb  the  vertical  circulation  Ijy 
alternately  impelling  and  retarding  one  or  the  other  of  the 
descending  and  ascending  columns  of  heated  matter,  thus 
occasioning  great  irregularity.  (4)  The  periodic  change  of 
position  of  the  centre  of  gravity  of  the  aggregate  planetaiy 
mass  must  necessarily  produce  a  periodic  maximum  and 
minimum  disturbance  of  the  descending  and  ascending  cur- 
rents ^vithIn  the  solar  mass.  It  will  be  evident  that  the 
frerpient  near  approach  and  consequent  powerful  attraction 
of  Venus  greatly  complicates  the  question  of  maximum  dis- 
turbance. (5)  The  rotation  of  the  sun,  it  should  be  parti- 
cularly observed,  tends  to  mollify  the  disturbing  influence  of 
planetary  attraction  on  the  vertical  circulation,  since,  owing 
to  this  rotation,  the  descending  and  ascending  motion  of  the 
heated  matter  within  the  solar  mass  is  successively  relieved 
from  maximum  disturbing  iufluence  twice  in  twenty-five 
days.  It  may  be  sho^vn  that,  but  for  this  frequent  check, 
the  power  exercised  by  planetary  attraction  would  aug- 
ment, and  fatally  derange  the  internal  circulation  indispen- 
sable to  the  regular  performance  of   the  functions  assigned 


CHAP.  vii.  THE  SOURCE  OF  SOLATi  ESEliGT.  151 

to  the  sun.  (0)  It  neetl.s  no  cxiilmiation  that  a  continuous 
disturbance  and  consequent  cessation  of  circuhition  at  certain 
jioints  of  the  solar  .surface  would  produce  permanent  dark 
spots.  Bearing  in  mind  the  enormous  amount  of  the  regular 
emission  of  heat  demonstrated  in  Chap.  V.  (;522,000  thermal 
units  per  minute  on  a  square  foot  of  the  solar  surface),  it 
becomes  evident  that  any  considerable  diminution  of  the 
^"PPb'  o^  energy  from  within,  consequent  on  deranged  cir- 
culation, will  at  once  produce  a  great  fall  of  temperature  at 
the  surface  of  the  photosphere,  and  a  corresponding  diminu- 
tion of  the  temperature  of  the  contiguous  solar  atmosphere, 
accompanied  by  a  sudden  condensation  and  do\\n-rush  ovei- 
the  regions  of  t>bstructed  circulation.  Considering  the  in- 
creased Aveight  of  the  condensed  matter  put  in  motion  l)y 
the  sun's  powei-ful  attraction,  we  can  readily  imagine  that 
the  photosphere,  suspended  over  the  solar  mass,  as  supposed 
by  Lockyer,  may  be  pierced  by  the  descending  column,  and 
an  opening  formed,  exposing  that  part  of  the  solar  mass 
which,  for  want  of  circulation  and  supply  of  heat  from 
within,  has  lost  intensity  and  radiant  power.  It  should  be 
observed  that,  although  we  have  no  knowledge  of  the  con- 
stitution of  the  photosphere,  we  may  assert  positively  that 
its  radiant  power  is  derived  from  the  underlying  solar  mass, 
and  that,  therefore,  any  diminution  of  energy  of  the  lattci-, 
occa.sioned  by  disturbed  circulation,  will  at  once  diminish  the 
tenqierature  and  radiant  power  of  that  portion  of  the  photo- 
sphere which  is  situated  above  the  obstruction.  (7)  The 
descending  and  ascending  columns  of  heated  matter  between 


152  EABIANT  HEAT.  chap.  vii. 

the  solar  centre  and  tlie  poles,  being  acted  upon  almost  at 
right  angles  by  planotarv  attraction,  remain  at  all  times  nearly 
undisturbed  ;  hence  only  a  few  dark  spots,  of  small  size,  form 
in  the  polar  regions. 

Regai'diug  the  permanency  of  solar  radiation,  the  forego- 
ing explanations  show  that  the  system  of  veitioal  circulation, 
upon  which  depends  the  efficiency  of  the  sun  as  a  motor, 
may  become  deranged.  The  consequence  of  this  precarious 
feature  of  the  scheme  is  self-evident,  if  we  consider  that  the 
present  solar  emission  is  dependent  on  a  given  rate  of  contrac- 
tion of  the  solar  mass.  Should  that  contraction  be  checked 
by  interrupted  circulation,  the  development  of  heat  will  also 
l)e  checked,  and,  consequently,  the  intensity  of  solar  radiation 
become  inadequate  to  sustain  animal  and  vegetable  life,  as 
now  organized,  on  our  planet.  History  informs  us  that  the 
luminary  has  at  certain  epochs  partially  failed  to  pei'foi'm 
its  functions.  Hei-schel  mentions,  in  his  "  Outlines  of  Astro- 
nomy," that  "  in  the  annals  of  the  year  a.d.  536  the  sun  is 
said  to  have  suffered  a  great  diminution  of  light,  which  con- 
tinued fourteen  months.  From  October  a.d.  626  to  the  fol- 
lowing June  a  defalcation  of  light  to  the  extent  of  one-half 
is  recorded  ;  and  in  a.d.  1547,  during  three  days,  the  sun  is 
said  to  Lave  been  so  darkened  that  stars  were  seen  in  the 
day-time."  Again,  the  glacial  periods,  the  ascertained  abrupt 
termination  and  recurrence  of  which  puzzles  the  geologist, 
point  to  periodical  derangement  of  the  solar  mechanism  iu 
past  ages. 


CHAPTER  VIII. 


RAl)lAriX(i    FOWKli  AXD   DEI'l'lI   OF   THE   SOLAE 
ATMOSFllEKE. 


Tin:  illustration  shoA^Ti  on  Plate  15  represents  an  instini- 
nient  constructed  for  the  purpose  of  asccrtnininy  the  radiant 
[lower  of  the  sohir  atmosphere,  and  for  measuring  its  depth, 
the  leading  feature  i>f  the  device  being  that  of  shutting  out 
the  rays  h\m\  tlic  pliutosjihere  during  the  investigation.  Evi- 
dently the  expedient  of  shutting  out  tlie  photi'sphere  while 
examining  the  effect  produced  by  the  i'a}s  emanating  from 
the  solar  envelope  calls  for  means  by  which  the  sun  may  be 
kept  accurately  in  focus  during  the  period  i-equired  to  com- 
jilete  the  observations.  The  main  features  of  tlie  instrument 
being  clearly  shown  by  the  illustration,  a  brief  description 
■will  be  sufficient  to  explain  its  detail.  A  jiarabolic  reilector, 
applied  for  the  purpose  of  concentrating  the  rays  of  the  solar 
atmosphere,  is  inserted  in  the  cavity  of  a  conical  dish  of  cast 
iron,  secured  to  tlie  top  of  a  table  suspended  on  two  hori- 
zontal journals,  and  revolving  on  a  vertical  axle.  The  latter, 
slightly   taper,   turns   in  a  oastirou   socket,   which   is   bushed 

Hi 


154  HADIAST  HEAT.  CHAP.  vill. 

witli  lii'ass  and  supj)orte(l  l)y  tlirt'c  legs  stepped  on  a  trian- 
gnlar  l)ase,  resting  on  fi'letion-rollers.  The  liori/.ontal  jour- 
nals referred  to  turn  in  bearings  attached  to  a  rigid  Lar  of 
wrought  iron  situated  under  the  table,  fii-ndy  secured  to  the 
upper  end  of  the  vertical  axle.  The  horizontal  angular  posi- 
tion of  the  taltle  is  adjnsted  by  a  screw  operated  by  the 
small  hand-wheel  a,  the  inclination  being  regulated  by  an- 
other screw  turned  by  the  hand-wheel  h.  A  gradiuxted  quad- 
rant, e,  is  attached  to  the  end  of  the  table  in  order  to 
afford  means  of  ascertaining  tlie  sun's  zenith  distance  at  any 
moment.  The  index  cl,  which  marks  the  degree  of  inclina- 
tion, is  stationary,  being  secured  to  the  rigid  bar  before 
described.  The  rays  from  the  photosphere  are  shnt  out  l)y 
a  circular  disc  _/',  composed  of  sheet  metal  turned  to  exact 
size,  and  supported  by  three  diagonal  rods  of  steel.  These 
rods  are  secured  to  the  circumference  of  the  conical  dish  by 
screws  and  adjustal:)le  nuts  in  such  a  manner  that  the  centre 
of  the  disc  /  may  readily  be  brought  in  a  direct  line  "with 
the  axis  of  the  reflector.  The  mechanism  adopted  for  adjust- 
ing the  position  of  the  tal)le  by  the  hand-wheels  a  and  h 
requires  no  explanation  ;  but  the  device  which  enables  the 
operator  to  ascertain  when  the  axis  of  the  reflector  is  pointed 
exactly  towards  the  centre  of  the  sun  demands  particular 
notice.  A  shallow  cylindrical  box  (j,  provided  ^\ith  a  flat 
lid  and  open  at  the  bottom,  excepting  a  narroAV  flange  extend- 
ing rouud  the  circumference,  is  firmly  held  by  two  columns 
secured  to  the  top  of  the  table.  A  convex  lens  of  26  ins. 
focus   is  inserted    in    the  (!}liudricul   box,   the   narrow   flange 


cuAi'.  VIII.    i;.\i>iATi\(!  I'owKi:  or  sola  I!  ATMosriii:!;!-:.       155 

meutioued  affoidiug  necessary  supixirt.  'llir  li<l  is  perfo- 
rated by  two  opeuings  at  right  angles,  (iji.")  in.  wide,  l\5 
ins.  long,  forming  a  cross,  tlie  lens  being  so  adjusted  that 
its  axis  passes  tlirough  the  central  point  of  intersection  of 
the  cross.  The  face  of  the  table  being  tnrned  at  right 
angles  to  the  sun,  or  nearly  so,  it  will  be  evident  that  the 
rays  passing  through  the  pei-forations  and  through  the  lens 
will  produce,  at  a  certain  distance,  a  brilliantly  illuuiiuat.Ml 
cross  of  small  size  and  sharp  outline.  A  piece  of  ivory,  on 
which  parallel  lines  are  drawn  intersecting  each  other  at 
right  angles,  is  attached  to  the  top  of  the  table  in  such  a 
position  that  the  centre  of  intei-section  of  the  said  lines  coin- 
cides with  the  axis  of  the  lens.  This  axis  being  parallel 
with  the  line  passing  through  the  centre  of  the  disc  /  and 
the  focus  of  the  reflector,  it  Avill  be  perceived  that  the  ope- 
rator,  in  directing  the  table,  has  oidy  to  bring  the  illuminated 
cross  within  the  intersecting  parallel  lines  on  the  piece  of 
ivory.  Ample  practice  has  sho^vn  that  by  this  arrangement 
an  attentive  person  can  easily  keep  the  disc  /'  accurately  in 
line  with  the  focus  of  the  reflector  and  the  centre  of  the 
sun  during  any  desirable  length  of  time.  The  absence  of 
any  perceptible  motion  of  the  column  of  the  f<x-al  thermo- 
meter employed  during  the  e.xperiiiK  iits  furnishes  the  l^est 
evidence  that  the  sun's  rays  have  been  effectually  shut  out 
by  the  intervening  disc  /;  which,  it  should  be  remembered, 
is  only  large  enough  to  screen  the  aperture  of  the  reflector 
from  the  rays  projected  l»y  the  photosj.here.  It  is  woithy 
of  observation   that   the   lightness  of  the  adopted   mechanism 


156  RADIAST  HEAT.  CHAP.  viii. 

renders  exact  iuljustiueut  easy,  since  screws  of  small  diameter 
and  tine  pitch  may  be  employed.  It  is  hardly  necessary  to 
point  out  that  the  table  represented  by  our  illustration  is 
admirably  adapted  for  actinometric  observations,  since,  apart 
from  its  perfect  parallactic  motion,  it  is  provided  with  a  cpiad- 
rant  and  index  sho\\ing  the  sun's  zenith  distance. 

Fig.  2  (see  Plate  16)  represents  a  vertical  section  of  the 
parabolic  reflector  before  adverted  to,  inserted  in  the  cast-iron 
dish  attached  to  the  parallactic  table.  This  I'etiector  consists 
of  a  solid  wrought-iron  ring  lined  -with  silver  on  the  inside, 
turned  to  exact  form  and  highly  polished.  An  annular  plate 
U.5  ins.  internal  diameter  is  secured  to  the  top  of  the  wrought- 
iron  ring,  in  order  to  jjrevent  effectually  all  rays  projected  by 
the  photosphere  from  reaching  the  reflector. 

The  important  cpiestion  whether  the  solar  envelope  pos- 
sesses an  appreciable  radiant  power,  and  whether  the  high 
temperature  of  the  attenuated  matter  of  which  it  is  composed 
exercises  any  marked  influence  on  the  sun's  radiant  energy, 
may  unquestionably  be  answered  practically  by  means  of  the 
instrument  thus  described.  I  have  accordingly  conducted  an 
investigation  based  on  the  expedient  of  concentrating  the  heat- 
rays  of  the  solar  atmosphere  by  the  parabolic  reflector  men- 
tioned, in  such  a  manner  that  only  the  heat-rays,  if  such  there 
be,  from  the  chromosphere  and  exterior  solar  envelope  are 
reflected,  while  the  rays  from  the  photosphere  are  effectu- 
ally shut  out.  Fig.  1  shows  the  general  ai'rangemeut;  /'  a' 
represents  the  exterior  of  the  photosi^here,  and  (j'  Ii  the  boun- 
dary of  the  surrounding  solar  atmosphere  ;  7t  /  is  the  circulai' 


cuAP.  VIII.    L'ADiATisa  I'owKi;  OF  s<n..\i:  .\'nrosrin:nr:.       157 

metallic  disc,  supported  above  the  parabolic  reflectoi'  before 
described,  and  marked  f  in  the  ilbistration  on  Plate  15.  This 
disc  is  exactly  !<•  ins.  in  diaiiifter,  placed  5.'^.7'>  ins.  above 
the  base  line  <^  o;  the  latter  (•oincidini;-  \\illi  the  top  of  the 
parabolic  reflector.  The  stated  distance  l)et\veen  the  disc 
and  the  top  of  the  reflector  obvionsly  varies  considerably 
uith  the  seasons.  Assumincf  that  the  investimition  takes 
place  when  the  sun  subtends  an  angle  of  32  min.  1  sec, 
and  making  proper  allowance  for  diffraction,  the  disc  k  7,  if 
placed  53. 7()  inches  from  a  o,  will  throw  a  shadow  of  fully 
i*.5  ins.  diametei' ;  hence,  if  /'  o  be  9.5  inches,  objects  in  the 
plane  </  c,  placed  within  /'  o,  will  ])e  effectually  shut  out 
from  the  rays  projected  by  the  photosidiere,  while  they  will 
be  fully  exposed  to  the  rajs  (/'  g  and  7/  //,  emanating  from 
the  chromosphere  and  outer  strata  of  the  solar  enve]o[)e.  It 
is  evident,  therefore,  that  a  parabolic  reflector  of  ])ro[)er  size 
placed  immediately  below  /'  n  will  concentrate  the  radiant 
heat,  if  any,  transmitted  by  the  rays  f  f  and  <j'  ;/,  and  the 
intermediate  rays.  It  has  already  been  stated  that  an  an- 
nular plate  9.5  ins.  internal  diameter  is  secured  to  the  top 
of  the  reflector  to  i)revent  effectually  any  rays  projected  by 
the  photosphere  from  reaching  the  same.  'J'he  prolongation 
of  the  rays  f  f  —  (/'  'J  :uid  /(  n  —  a'  o  are  shown  by  dotted 
lines  /*,  g  and  n,  o  in  Fig.  2  ;  also  the  reflected  rays  directed 
towards  the  bulb  of  the  focal  thermometer,  marked  resjiec- 
tively /\  o'  and  g\  it'. 

The  following  brief  account  is  deemed  sufficient  to  ex])laiii 
the  mode  of  conductiiiir  the  investigation:  TuriiiiiLr  the  reflec- 


158  EADIAXT  HEAT.  chat.  vin. 

tor  towards  tlie  sun,  w  itliuut  applying'  thu  disc  l  /,  it  will 
be  found  that  a  naiiow  zone  of  dazzling  \vliite  light  is  pro- 
duced on  the  black  bulb  of  the  focal  thermometer  p,  the 
mercurial  column  commencing  to  rise  the  moment  the  rays 
strike  the  reflecting  surface.  With  a  perfectly  clem'  sky,  the 
column  has  been  found  to  reach  320  deg.  Fall,  in  35  sec. 
The  screen  !•  /  being  applied  after  cooling  the  thermometer, 
a  zone  of  feeble  gray  light  appears  on  the  black  bulb  nearly 
as  deep  as  the  one  produced  by  the  rays  froin  the  photo- 
sphere, but  situated  somewhat  lower.  The  column  of  the 
focal  thermometer  invariably  remains  stationary,  excejiting 
the  oscillation  which  always  takes  place  when  a  thermo- 
meter is  subjected  to  the  influence  of  the  currents  of  air 
unavoidable  in  a  place  exposed  to  a  powerfid  sun.  It  is 
proper  to  remark  that,  owing  to  the  stated  oscillation,  it 
cannot  be  positively  asserted  that  no  heating  whatever  has 
been  produced  by  the  reflection  and  concentration  of  the 
raj's  which  fonu  the  zone  of  gray  light  adverted  to.  But 
the  recorded  oscillations  prove  absolutely  that  the  heating 
does  not  exceed  0.5  deg.  Fah. 

Assuming  that  a  temperature  of  0.5  deg.  Fah.  has  actu- 
ally been  produced  by  the  reflected  concentrated  heat  ema- 
nating from  the  solar  envelope,  the  following  calculation  \\  ill 
show  that  the  energy  thereby  established  is  too  insignificant 
to  exercise  anj-  appireciable  influence  on  the  sun's  radiant 
power.  Theoretically,  the  temperature  transmitted  to  the 
bulb  of  the  focal  thermometer  by  the  reflection  of  the  rays 
/  and  0,  Fig.  2,  is  as  the  foreshortened  illuminated  area  of 


CH  A  I".  VIII.     RAl>fATfX(l  I'OWEli  Ol-i^OL.yn  ATMOSl'IlKUi:.  loH 

the  ivrtector  to  the  aiva  of  tlie  zone  of  light  pimliU'L-d  on 
the  bulb.  Obviously  these  areas  bear  nearly  the  same  rela- 
tion to  each  othei"  as  the  squares  of  f  or  u'  to  the  square  of 
the  radius  of  the  bulb  ji.  The  length  of  _/'  being  4.77  ins., 
while  the  radiu.s  of  the  bulb  is  0.12.")  in.,  calculation  shows 
tliat  the  temperature  transmitted  by  the  ray  /  would  be 
increased  1,45G  times  if  the  reflectoi'  did  not  absorli  anv 
heat.  Allowing  that  (>.7l^  of  the  heat  is  reflected,  the  aug- 
mentation of  intensity  by  concentration  will  amount  to  0.72 
X  1,456  =  1,048  times  the  temperature  transmitted  by  the 
rays  /  and  o.  The  records  of  the  oscillations  of  the  mercu- 
rial column  during  the  experiments  show,  as  stated,  that 
the  temperature  resulting  from  concentration  caiHH)t  exceed 
0.5  deg. ;  hence  the  temperatuie  transmitted  by  the  rays 
emanating  from  tlie  heated  matter  of  the  solar  envelope  will 

only  amount   to  — ^   =  U.U0047   deg.   F;ili.      The    recorded 

observations  having  been  made  when  the  sun's  zenith  dis- 
tance was  32  deg.  15  min.,  a  correction  for  loss  occasioned 
by  atmospheric  absorption  amounting  to  0.2G  will,  hinvever, 
be  necessaiy.  This  correction  being  made,  it  will  be  found 
that  the  heat  actually  transmitted  by  the  I'ays  from  the  solar 
enveloj^e  during  the  experiment  referred  to  did  not  exceed 
0.00059  deg.  Fah. — a  fact  which  completely  disposes  of 
Secchi's  remarkable  assumption  that  the  high  temperature 
of  the  photosphere  is  owing  to  the  "  radiation  received  from 
all  the  transparent  strata  of  the  solar  envelope"  (see  his 
letter  to  Xatun,  published  June   1,   1671). 


IGO  HABIAXT  HEAT.  chap.  viii. 

Having  tlius  positively  established  the  fact  that  no  appre- 
ciable heat  is  transmitted  to  the  earth  by  the  radiant  power 
of  the  solar  atniosj^here,  and  thereby  disposed  of  Secchi's 
erroneous  assumptions,  and  proved  the  unsoundness  of  the 
views  entertained  by  other  physicists  that  "  the  regions  near 
the  sun  augment  the  radiant  energy  transmitted  by  the  lumi- 
nary," let  us  now  consider  the  probable  weight  and  depth 
of  the  solar  atmosphere.  The  investigation  will  be  greatly 
facilitated  by  instituting  a  comparison  between  the  sun's 
envelope  and  the  terrestrial  atmosphere,  and  by  adoj)ting 
as  a  basis  in  our  calculation  the  fact,  established  in  Chap. 
X.,  that  the  temperature  at  the  surface  of  the  photosphere, 
and  hence  that  of  the .  contiguous  solar  atmosphere,  exceeds 
4,000,000  deg.  Fah.  The  fallacy  of  Dulong  and  Petit's  for- 
mula relating  to  the  rate  of  cooling  of  incandescent  matter 
at  high  temperatures,  and  its  consequent  inapplicability  to 
the  question  of  solar  temperature,  having  been  fully  demon- 
strated in  Chap.  II.,  Avhile  our  actinometric  observations 
recorded  in  Chap.  III.  have  established  the  intensity  of 
solar  radiation  at  the  boundary  of  the  terrestrial  atmosphere, 
we  possess,  it  should  be  borne  in  mind,  the  elements  neces- 
sary to  prove  the  correctness  of  the  assumed  high  degree  of 
solar  temperature.  As  before  stated,  our  investigation  wall 
be  simplified  by  comparing  the  solar  and  terrestrial  atmo- 
spheres ;  hence  the  following  mode  of  solving  the  important 
problem :  The  increase  of  the  volume  of  atmospheric  air, 
under  constant  pressure,  being  directly  proportional  to  the 
increment  of  temperature,  while  the  coefficient  of  expansion 


CHAP.  VIII.     RADIATIXG  POWER  OF  SOLAR  ATMOHI'IIERE.         ICl 

is  0.00203  deg.  for  1  deg.  of  Faliiviiheit,  it  will  he  found 
by  calculation  that  3,272,000  deg.  Fall,  (that  being  the  mean 
temperature  of  the  solar  atmosphere)  communicated  to  the 
terrestrial  atmosphere  would  reduce  its  density  to  Wrj  of 
the  existing  density.  Accordingly,  if  we  assume  that  the 
height  of  our  atmosphere  is  only  42  miles,  the  elevation  of 
temperature  mentioned  would  cause  an  expansion  increasing 
its  height  to  6,643  X  42  =  270,000  miles.  This  calculation, 
it  should  be  observed,  takes  no  cognizance  of  the  diminution 
of  the  earth's  attraction  at  great  altitudes,  which,  if  taken 
into  account,  would  considerably  increase  the  estimated 
height.  Let  us  now  snj^pose  the  atmosphere  of  the  sun  to 
be  replaced  by  a  medium  similar  to  the  terrestrial  atmo- 
sphere raised  to  the  temperature  of  3,272,000  deg.  Fah.,  and 
containing  the  same  quantity  of  matter  as  the  terrestrial 
atmosphere  for  coiTesponding  area  of  the  solar  surface.  Evi- 
dently the  attraction  of  the  sun's  mass  would,  under  these 
conditions,  augment  the  density  and  weight  of  the  supposed 
atmosphere  nearly  in  the  ratio  of  27.9  :  1 ;  hence  its  height 

, ,    ,  ,       ,  279,006 

would    be   reduced   to       ^^  ^     =  10,000   miles.     But   if   the 
27.9 

atmosjihere  thus  increased  in  density  by  the  sun's  superior 
attraction  consisted  of  a  compound  gas,  principally  hydro- 
gen, say  1.4  times  heavier  than  pure  hydrogen  (the  specific 
weight  of  ^vhich  is  only  tV  of  that  of  atmospheric  air),  the 
height  would  be  10  X  10,000  =  100,000  miles.  The  pres- 
sure exerted  by  this  supposed  atmospliere  at  the  surface  of 
the  photosphere  would  obviously  be  14.7  X  27.9  =  410  lbs. 


162  E AVIAN T  HEAT.  chap.  yiii. 

per  sq.  in.  nearly.  It  will  be  observed  that  our  computa- 
tions are  based  on  a  solar  attraction  of  27.9,  instead  of  the 
recent  estimate  of  27.2.  The  foregoing  calculations  prove 
that,  unless  the  depth  greatly  exceeds  100,000  miles,  and 
unless  it  can  be  shown  that  the  mean  temperature  is  less 
than  3,272,000  deg.  Fah.,  the  important  conclusion  must  be 
accepted  that  the  solar  atmosphere  contains  an  exceedingly 
small  quantity  of  matter.  Now,  the  assumed  mean  teuqie- 
rature,  3,272,000  deg.  Fah.,  so  far  from  being  too  high,  w\Y[ 
be  found  to  be  underrated.  It  will  be  seen,  on  reference  to 
Chap.  X.,  that  the  temperature  at  the  surface  of  the  photo- 
sphere, determined  in  accordance  Avith  well-ascertained  ele- 
ments, somewhat  exceeds  4,035,000  deg.  Fah.  Consequently, 
as  the  diminution  of  intensity  caused  by  the  dispersion  of 
the  rays  is  inversely-  as  the  convex  area  of  the  photosphere 
and  that  of  the  sj)here  formed  by  the  boundaiy  of  the  solar 
envelope — namely,  as  1.52  :  1 — imder  the  supposition  that  the 
depth  of  the  solar  atmosphere  is  100,000  miles,  the  tempera- 

•1.  ,      4,035,000 

ture  at  the  said  boundary  will  be  =  2,654,000  deer. 

•  1.52  ° 

The  true  mean,  therefore,  will  be  3,344,800   deg.,  instead  of 

3,272,000   deg.   Fah. — a  difference  which  leads  irresistibly  to 

the  inference  that  either  the  sun's  atmosphere  is  more  than 

100,000   miles   in  depth,  or  it  contains  less  matter  than  the 

terrestrial    atmosphere    for    corresponding    area   of   the    solar 

surface.     The  ratio  of  diminution  of  the  density  of  the  gases 

composing   the   solar    atmosphere    at   succeeding   altitudes    is 

represented    by   Fig.    3,    in    Avhich    the    length    of   the    oi'di- 


CHAP.  VIII.     RADIATIM!  POWER  OF  tiOLAlt  ATMOHl'll EliE.         IC.'i 

nates  of  tlie  curve  a  d  h  sLows  the  degree  of  teuuity  at 
definite  points  above  the  photosphere.  This  curve  has  been 
constructed  agreeably  to  the  theory  tliat  the  densities  at  dif- 
ferent altitudes,  or,  what  amounts  to  tlie  same,  the  weight  of 
the  masses  incumbent  at  succeeding  points,  decreases  in  geo- 
metrical progression  as  the  height  above  the  base  increases 
in  arithmetical  progression.  The  vertical  line  a  c  has  been 
divided  into  42  equal  parts,  in  order  to  facilitate  compari- 
sons with  the  terrestrial  atmosphere,  supposed  to  be  4:2  miles 
deep,  the  relative  density  of  which,  at  corresponding  heights, 
is  obviously  as  correctly  represented  by  our  diagram  as  that 
of  the  solar  atmosphere.  It  is  true  that,  owing  to  the  greater 
height  of  the  latter  compared  with  the  attractive  force  of  the 
sun's  mass,  the  upper  strata  of  the  terrestrial  atmosphere  will 
be  relatively  more  powerfully  attracted  than  the  upper  strata 
of  the  vastly  deeper  solar  atmosphere.  The  ordinates  of  the 
curve  a  d  h  will  therefore  not  represent  the  density  quite 
correctly  in  both  cases.  The  discrepancy,  however,  resulting 
from  the  I'elatively  inferior  attraction  of  the  sun's  mass  at 
the  boundary  of  its  atmosphere  will  be  very  nearly  neutral- 
ized by  the  increased  density  towards  that  boundary,  conse- 
quent on  the  great  reduction  of  temperatui-e — fully  1,380,000 
deg.  Fah. — caused  by  the  dispersion  of  the  solar  rays  before 
entering  space.  It  may  be  Avell  to  state  that,  in  representing 
the  relative  height  and  pressure  of  the  terrestrial  atmosphere, 
a  c  in  our  diagram  indicates  42  miles,  while  h  c  indicates  a 
pressure  of  14.7  lbs.  per  s(p  in.  ;  and  that,  in  representing 
the  solar  atmosphere,  a  c  indicates   100,000   miles,   anil   l>  c 


164  BADIANT  HEAT.  chap.  vm. 

410  lbs.  per  stp  in.  Beariug  in  miud  tlie  liigb  temperature 
and  the  exceedingly  small  specific  gravity  of  the  matter 
composing  tlie  solar  atmosphere,  the  exti'eme  tenuity  of  the 
higher  regions,  indicated  by  the  ordinates  sho-wn  in  the  dia- 
gram, will  be  readily  comprehended.  Calculation  shows  that 
towards  the  assumed  boundary  the  density  of  the  solar  atmo- 
sphere is  so  far  reduced  that  it  contains  -only  to^Wo  of  the 
quantity  of  matter  contained  in  an  equal  volume  of  atmo- 
sphere at  the  surface  of  the  earth. 

The  diminution  of  intensity  consequent  on  the  increased 
depth  of  the  solar  atmosphere  through  which  the  calorific 
rays  pass,  which  are  projected  towards  the  earth  from  the 
receding  surface  of  the  photosphere,  having  been  considered 
in  Chap.  VI.,  it  will  only  be  necessary  to  mention  in  this 
place  that  Fig,  4  represents  the  sun,  and  its  atmosphere 
extending  i  of  the  semi-diameter  of  the  photosphere,  ni  h, 
c  g,  etc.,  being  the  rays  projected  towards  the  earth.  The 
depth  of  the  solar  atmosphere  at  a  distance  of  ii  of  the 
radius  from  the  centre  of  the  luminary,  it  will  be  seen, 
amounts  to  only  2.0012  of  that  of  the  vertical  depth.  It  is 
hardly  necessary  to  observe  that  the  radiant  energy  trans- 
mitted by  the  ray  c  d  will  be  to  the  energy  transmitted  by 
a  ^  as  the  sine  of  the  angle  f  c  d  to  unity. 

The  foregoing  reasoning  demonstrates  that  the  solar  atmo- 
sphere, owing  to  its  enormous  temperature,  may  reach  a  height 
of  100,000  miles  and  yet  not  contain  more  matter  on  a  given 
area  of  the  sun  than  the  terrestrial  atmosphere  on  an  equal 
area.     I  have  endeavored  to  verify  this  important  conclusion 


CHAP.  VIII.     TiATUATISG  POWEU  OF  .SOLA  h'  ATMOSI-IJIJI.'E.  Ifio 

piactifiilly,  and  for  that  purpose  resorted  to  the  expedient 
of  enlarging  the  disc/  (see  illustration  on  Plate  15)  until  the 
spectrum  disappear  which  is  formed  on  the  focal  thermo- 
meter by  the  concentration  of  the  rays  emanating  from  the 
sun's  atmosphere.  It  should  be  stated  that  the  original  object 
of  the  instrument  illustrated  was  merely  that  of  ascertaining 
whether  the  incandescent  matter  contained  in  the  solar  atmo- 
sphere transmits  radiant  heat  of  sufficient  energy  to  admit  of 
thenuometric  measurement.  But  the  appearance  of  a  sjiec- 
trum  on  the  bulb  of  the  focal  thermometer,  after  shutting 
out  the  rays  from  the  photosphere,  suggested  the  expedient 
of  substituting  for  the  thermometer  a  small  cylindrical  stem 
of  metal,  coated  with  lamp-black,  in  order  to  ascertain  Avith 
some  degree  of  i>recision  what  amount  of  enlargement  of  the 
disc  /'  is  necessaiy  to  exclude  the  focal  spectrum,  as  bj-  that 
means  the  depth  of  the  sun's  atnicsphere  might  be  measured. 
The  result  of  the  observation  proves  that  while  a  disc  of  10 
ins.  diameter  effectually  shuts  out  the  rays  from  the  photo- 
sphere, an  enlargement  of  about  0.15  inch  of  the  radius  of 
the  disc  is  necessaiy  to  exclude  completely  the  observed  spec- 
trum from  the  focal  stem.  Now,  the  distance  between  the 
spectrum  and  the  disc  being  53.7  ins.,  it  will  be  found  by 
calculation  that  the  stated  enlargement  of  the  disc  corresponds 
with  an  angular  distance  of  9'  45";  hence,  assuming  the  radius 
of  the  photosphere  to  be  426,000  miles,  the  depth  of  the  mea- 
surable part  of  the  solar  envelope  cannot  be  less  than  255,000 
miles. 


CHAPTER   IX. 


THE  FEEBLENESS  OE  SOLAR  RADIATION  DEMONSTRATED. 


It  is  a  remarkable  fact  tliat  some  of  tlie  most  prominent 
scientists  entertain  wholly  incorrect  views  regarding  the  sun's 
radiant  intensity.  Apparently,  they  are  not  aw^are  that  the 
temperature  produced  by  unaided  solar  radiation  is  fully  300 
deg.  Fahrenheit  below  the  freezing-point  of  water.  Sir  John 
Herschel,  in  discussing  the  increase  of  the  intensity  of  solar 
radiation  consequent  on  the  reduced  distance  from  the  sun 
when  the  earth  is  in  perihelion,  presents  the  following  views : 
"  In  estimating  the  effect  of  any  additional  fraction,  as  ont- 
jifteenth,  of  solar  radiation  on  temperature  (this  fraction  being 
determined  by  applying  the  law  of  inverse  squares  to  the  dimi- 
nution of  the  sun's  distance  when  the  earth  is  in  perihelion), 
we  have  to  consider  as  our  unit,  not  the  niimber  of  degrees 
above  a  purely  arbitrary  zero-point — such  as  the  freezing- 
point  of  water  or  the  zero  of  Falirenheit's  scale — on  which 
a  thermometer  stands  in  a  hot  summer  day,  as  compared 
with  a  cold  winter  one,  but  the  thermometric  interval  between 


CHAP.  IX.        THE  FEEBLENESS  OF  SOLAE  liADIATIOX.  167 

t/ie  temperature  it  indicates  in  the  two  cases  and  that  which 

it  would  indicate  did  the  sun  not  exist,  which  there  is  good 

reason  to  believe  would  be  at  least  as  low  as  239°  below 

zero  of   Fahrenheit.      And  as  a  temperature  of    100°   above 

zero  is  no  uncommon  one  in  a  fair  shade  exposui-e  under  a 

sun  nearly  vertical,  we  have  to  take  one-fifteenth  of  the  sum 

/239  +  100\ 

of  these  intervals  ( )  =  23^  Fahrenlieit,  as  the  least 

\         15        ' 

variation  of  temperature  under  siich  circumstances  Avhich  can 
reasonably  be  attributed  to  the  actual  variation  of  the  sun''s 
distancey  It  will  be  observed  that  the  foregoing  quotation 
has  partially  appeared  in  a  preceding  chapter,  yet  it  could 
not  be  omitted  in  this  place  without  rendering  the  demon- 
stration incomplete.  Considering  that  "absolute  zero"  (ascer- 
tained in  the  meantime)  Is  460°  below  the  zero  of  Fahrenheit 
instead  of  239°,  as  supposed  by  Herschel,  it  will  be  seen 
that,  according  to  his  doctrine,  the  increase  of  temperature 
resulting  from  the  su)\!s  proximity  irhen  the  earth  is  in  peri- 

helion  shoidd  be  =  37°  F.     Referring  to  Chap. 

15 

IV.,  it  will  be  found  that  solar  intensity  at  the  atmospheric 
boundaiy  is  90°.72  F.  during  the  winter  solstice,  and  that  the 
increase  of  the  radiant  intensity  at  that  time,  owing  to  the 
sun's  proximity,  is  4°.66  F.,  besides  the  loss  of  energy,  0.207, 
caused  by  atmospheric  absorption,  together  5°.88  F.,  instead 
of  37°  F.  This  extraordinary  discrepancy  is  the  result  of  Sir 
John  Hei-schel's  misapprehension  of  solar  intensity.  He  sup- 
poses, as  we  have  seen,  that  the  enei-gy  required  to  raise  the 


168  EADIANT  HEAT.  chap.  IX. 

temperature  from  absolute  cold  to  Fabreiilielt's  zero,  added  to 
the  energy  uecessary  to  raise  tlie  tempei'ature  from  tbat  zero 
to  the  j)oiut  reached  on  the  Fahrenheit  scale,  indicates  the 
tnie  intensity  of  the  radiant  heat ;  hence  460',  in  addition  to 
the  90°.72  before  mentioned,  together  550°.72  F.,  instead  of 
90°.72  F.  Referring  again  to  Chap.  IV.,  it  will  be  found 
that  the    intensity  of   solar  radiation  when  the   earth   is    in 

n    T       •     o.o        ■..      1  n  MT   .      'J0.72  +  84.84 

aphelion  is  84  .84  b. ;  hence  the  mean  will  be  

2 

=  87°.78  F.  Now,  the  mean  distance  of  the  earth  from  the 
sun's  centre  being  91,430,000  miles,  it  will  be  perceiv^ed  that 
solar  intensity  at  that  distance  cannot  exceed  87°.78  Fali- 
renheit.  In  order  to  show  the  practical  result  of  this  deter- 
mination of  solar  intensity,  let  us  suppose  that  an  air-ther- 
mometer, suiTounded  by  some  permanent  gas  maintained  at 
a  temperature  of  100°  F.  above  absolute  zero,  be  exposed  to 
the  sun,  and  that  the  side  of  the  bulb  exposed  to  the  sun's 
rays  is  nearly  flat,  while  the  back  is  semi-spherical  and  effec- 
tually protected  by  non-conducting  substances.  It  needs  no 
demonstration  to  prove  that  the  said  thermometer  will  indi- 
cate 100  +  87.78  =  187°.78  F.  above  absolute  zero,  or  492 
—  187.78  =  304°.22  F.  below  the  freezing-point  of  water, 
although  exposed  to  the  full  energy  of  the  sun's  rays.  Per- 
sons assigning  a  high  teinjierature  to  the  surface  of  the  moon 
will  do  well  to  consider  the  important  fact  thus  established. 
A  moment's  reflection  will  convince  them  that,  but  for  the 
accumulation  of  heat  effected  by  the  intervention  of  the  ter- 
restrial atmosphere,  water   could   not   exist  in  a  fluid  state, 


ciiAP.  IX.        THE  FEEBLENESS  OF  SOLAR  UADIATION.  1G9 

aud  that  even  the  vertical  rays  of  the  sun  within  the  tro- 
pics would  not  possess  sufficient  power  to  retain  mercury  in 
a  fluid  state. 

It  has  been  asserted  by  physicists  that  the  differential 
temperature  shown  by  thermometers,  however  judiciously 
arranged,  does  not  furnish  a  reliable  indication  of  solar 
energy,  on  the  ground  that  when  the  supposed  maximum 
intensity  has  been  reached  the  temperature  of  the  bulb 
Italances  that  of  the  solar  heat,  thus  preventing  further  in- 
crement. The  radiating  power  of  the  heated  bulb,  it  is 
urged,  remains  undiminished,  while  the  differential  tempera- 
ture between  the  same  and  the  surrounding  medium  is  at  its 
maximum ;  consequently  promoting  maximum  loss  of  energy 
by  radiation.  In  order  to  test  practically  the  merits  of  this 
plausible  argument,  and  in  order  to  determine  the  tine  inten- 
sity of  solar  radiation,  I  have  constructed  the  instrument 
illustrated  on  Plate  17.  The  delineation  represents  a  ver- 
tical section  through  the  centre  line  of  the  instrument.  The 
leading  feature  of  the  device  is  that  of  applying  a  hollow 
revolving  sphere  (composed  of  very  thin  copper)  within  an 
exhausted  cylindrical  vessel.  This  revolving  sphere,  coated 
with  lamp-black  inside  and  outside,  is  exposed  to  the  sun's 
rays  admitted  through  a  thin  crystal  covering  the  open  end 
of  the  exhausted  vessel,  the  diameter  of  the  crystal  being 
equal  to  that  of  the  sphere.  The  exhausted  cylindrical  vessel, 
it  will  be  seen  by  inspecting  the  illustration,  is  surrounded  by 
an  external  casing,  water  of  a  given  temperature  being  circu- 
lated through  the  intervening  space.     The  sphere  is  caused 


170  BADIANT  HEAT.  OHAP.  IX. 

to  revolve  by  means  of  a  small  hand-wheel  attached  to  a 
hollow  stem  connected  with  the  sphere;  the  said  stem  tm-n- 
ing  in  an  air-tight  stufBng-box  applied  on  the  upper  side  of 
the  exhausted  vessel.  A  thermometer  is  inserted  through  the 
hollow  stem,  the  bulb,  coated  with  lamp-black,  occupjdng  a 
central  position  within  the  sphere.  Obviously  the  thermo- 
meter participates  in  the  rotary  motion  of  the  sphere  when 
turned  by  the  hand-wheel.  The  instrument  is  supported  on 
columns  secured  to  a  table  provided  with  parallactic  move- 
ment for  the  purpose  of  pointing  the  axis  of  the  exhausted 
cylindrical  vessel  towards  the  solar  centre.  The  water  circu- 
lated through  the  external  casing  of  the  instrument  is  main- 
tained at  a  constant  temperature  of  60°  F.,  a  vacuum  being 
kept  up  within  the  internal  vessel.  As  the  thermometer 
does  not  fit  air-tight  in  the  hollow  stem,  it  will  be  evident 
that  the  pressure  of  the  air  mthin  the  revolving  sphere  will 
at  all  times  balance  the  external  atmospheric  pressure.  Let  us 
now  institute  a  comparison  between  the  instrument  described 
and  the  ordinary  thermometer. 

The  convex  area  of  the  revolving  sphere  being  four  times 
greater  than  the  area  of  its  great  circle,  the  latter  being  equal 
to  the  area  of  the  pencil  of  rays  admitted  through  the  crystal, 
it  will  be  evident  that  the  refrigerating  surface  of  the  sphere 
is  foiir  times  greater  than  the  sectional  area  of  the  solar  rays 
which  supply  the  radiant  heat.  Accordingly,  if  the  surround- 
ing cylindrical  vessel  be  permitted  to  radiate  freely  towards 
the  centre,  the  temperature  retained  by  the  revolving  sphere 
thus  exposed  to  cold  radiation  from  all  points  will  be  only 


CHAP.  IX.        THE  FEEBLENESS  OF  SOLAIi  RADIATION.  171 

one-fourtL  of  the  temperature  capable  of  being  imparted  by 
the  pencil  of  rays  to  the  face  of  a  flat  disc  composed  of  some 
non-conducting  substance.  It  may  be  stated,  in  further  expla- 
nation of  the  foregoing  demonstration,  that,  since  the  surround- 
ing exhausted  vessel  is  maintained  at  a  constant  temperature 
of  60°  .F.,  it  will  radiate  heat  of  that  energy  towards  the 
sphere.  An  exchange  will  consequently  take  place  which  Avill 
prevent  maximum  temperature  being  attained  by  the  sphere 
unless  the  radiant  energy  transmitted  by  the  solar  rays  enter- 
ing the  instrument  be  four  times  greater  for  equal  area  than 
the  I'adiant  energy  of  the  heat-rays  projected  by  the  sphere 
towards  the  cold  enclosure.  It  follows  from  this  important 
proposition  that  the  temperature  acquired  by  the  revolving 
sphere  represents  only  one-fourth  of  the  intensity  of  the 
radiant  energy  actually  passing  through  the  crystal  of  the 
exhausted  cylindrical  vessel.  It  will  be  I'eadily  perceived 
that  the  temperature  of  the  air  vrithin  the  revolving  sphere 
correctly  represents  the  temperatiare  of  the  metal  composing 
the  same ;  also,  that  the  metal  itself,  owing  to  its  almost 
perfect  conductivity,  will  become  uniformly  heated  all  over. 
The  inserted  thermometer,  therefore,  will  show  the  tempera- 
ture of  the  revolving  sphere  sufficiently  near  for  the  object 
in  view.  As  already  demonstrated,  only  one-fourth  of  the 
radiant  heat  entering  through  the  ciystal  is  retained  by  the 
sphere ;  hence  the  thermometer  will  indicate  only  one-fourth 
of  the  actual  intensity  of  the  sun's  rays.  Accordingly,  if  we 
multiply  the  indication  of  the  thermometer  within  the  revolv- 
ing sphere  by  4,  we  ascertain  the  true  solar  intensity,  less  the 


ira  BADIANT  HEAT.  chap.  ix. 

heat  absorbed  by  the  crystal  covering  the  exhausted  vessel. 
The  result  of  careful  observation  has  proved  the  soundness 
of  the  foregoing  reasoning  and  demonstration.  The  conclud- 
ing investigation,  instituted  when  the  zenith  distance  was  30 
deg.  50  niin.,  established  the  fact  that  while  the  standard  aeti- 
nometer  indicated  a  solar  intensity  of  54°.57  F.,  the  thermo- 
meter within  the  revolving  sphere  indicated  a  differential 
temperature  of  13°.3  F.     According  to  our  theory,  it  should 

54.57 
have  indicated  — '- —  =  13°.  64  F.,  thus  showing  a  deficiency 

of  0°.34.  If,  however,  a  correction  be  introduced  adding  the 
proportion  of  heat  absorbed  by  the  crj'^stal — viz.,  0.066 — the 
stated  deficiency  of  temperature  will  be  more  than  balanced. 
This  apj)arent  inaccuracy  is  occasioned  by  the  radiation  of 
the  crystal  towards  the  sphere,  and  by  the  diminution  of 
the  radiating  surface  of  the  surrounding  vessel  at  the  point 
where  the  crystal  is  inserted.  The  last-mentioned  source  of 
error  may  be  easily  ascertained,  as  it  dejiends  on  the  solid 
angle  formed  by  straight  lines  drawn  from  the  circumference 
of  the  crystal  to  the  centre  of  the  sphere.  The  deficiency 
of  radiating  surface  ascertained  by  that  process  amounts  to 
0.012.  Proper  allo^vance  having  been  made  on  account  of 
these  sources  of  error,  it  was  foimd  during  the  concluding 
investigation  referred  to  that  the  temperatui'e  retained  by 
the  sphere  exposed  to  the  solar  heat  is  exactly  one-fourtli  of 
the  temperature  imparted  and  retained  by  the  bulb  of  an 
actinometer  simultaneously  exposed  to  the  sun.  It  is  im- 
portant to  observe  that  the  difference  between  the  intensity 


CHAP.  IX.        THE  FEEBLENESS  OF  SOLAH  UADTATTOX.  173 

of  the  radiant  heat  of  the  sun  and  the  tempei'ature  of  the 
metal  composing  the  sphere  was  54°.57  -  13''.64  =  40°.93  F. 
during  the  investigation ;  while  the  temperature  of  the  bull) 
of  the  actinometer  exposed  to  the  sun,  at  the  same  time,  bal- 
anced the  intensity  of  the  solar  heat.  This  fact  completely 
refutes  the  assertions  of  certain  physicists  before  referred  to. 
Regarding  the  actual  iiitensitij  of  solar  radiation,  no  further 
demonstration  is  needed  to  show  that  the  temperature  indi- 
cated by  the  thermometer  within  the  revolving  sphere,  mul- 
tiplied by  4,  determines  the  true  energy  of  the  sun's  radiant 
heat  at  the  surface  of  the  earth ;  not,  however,  including  the 
energy  lost  by  atmospheric  absoqition.  The  close  agreement 
between  the  indication  furnished  by  the  instrument  thus  exa- 
mined and  the  indications  of  the  actinometer  described  in 
Chap.  III.  proves,  it  is  satisfactory  to  observe,  the  reliable 
character  of  the  tables  of  solar  temperature  contained  in 
that  chapter  constructed  in  accordance  with  our  actinome- 
trie  observations.  It  remains  to  be  noticed  that,  before  the 
conception  of  a  dry  revolving  bull),  I  constructed  an  instru- 
ment for  determining  solar  intensity,  in  which  a  large  sta- 
tionary hulb,  filled  with  water  and  provided  with  an  internal 
rotating  paddle-wheel,  was  employed.  The  illustration  on 
Plate  18  represents  a  section  through  the  vertical  plane  of 
that  instrument.  Before  giving  a  description  of  the  same,  it 
will  be  well  to  present  an  outline  of  the  reasoning  Avhich 
led  to  its  construction. 

Suppose  a  small  spherical    body  of   perfect   conductivity 
and  radiating  power  to  be  suspended  witliiu  a  large   enclo- 


174  BABIANT  HEAT.  CHAP.  ix. 

sure  provided  Tvath  ca  perforation  in  the  direction  of  tLe 
sun,  of  sufficient  size  to  admit  a  pencil  of  rays  of  the  same 
diameter  as  the  spherical  body.  Suppose,  also,  that  the  tem- 
perature of  the  said  body  is  64°  F.  higher  than  the  temjje- 
rature  of  the  enclosure  and  the  air  contained  within  the 
same.  The  convex  area  of  a  sphere  being  four  times  greater 
than  the  area  of  its  great  circle,  while  the  area  of  the  great 
circle  of  the  sphere  which  we  have  imagined  corresj)onds 
exactly  with  the  sectional  area  of  the  pencil  of  rays  entering 
through  the  perforation  of  the  enclosure,  it  will  be  evident 
that  tbe  supposed  excess  of  temperature,  64°,  cannot  be 
maintained  unless  the  radiant  energy  of  the  sun's  rays  be 
four  times  greater  for  corresponding  area  than  the  radiating 
energy  of  the  sphere.  It  will  also  be  evident  that,  if  the 
assumed  excess  of  temperature  of  the  sphere  gradually  falls 
while  exposed  to  the  sun's  rays,  until  it  is  reduced  to  16° 
above  the  temperature  of  the  enclosure,  then  the  intensity 
of  the  sun's  rays  cannot  be  more  than  4  X  16  =  64°.  Bear- 
ing in  mind  that  the  section  of  the  pencil  of .  rays  which 
transmits  the  energy  is  only  0.25  of  the  convex  area  of  the 
radiating  sphere  which  receives  the  beat  and,  in  turn,  radi- 
ates that  heat  towards  the  enclosure,  we  cannot  question  the 
correctness  of  the  deduction  that,  assuming  the  rays  to  be 
parallel,  the  intensity  of  the  radiant  energy  which  enters 
through  the  perforation  of  the  enclosure  is  four  times  greater 
than  the  radiant  energy  wbicli  the  sphere  parts  with.  Again, 
the  intensity  of  the  radiant  heat  emanating  from  solid  bodies 
being  a  correct  index  of  dynamic  energy,  it  -svill  be  perceived 


CHAP.  IX.        THE  FEEBLENESS  OF  SOLAR  liADIAIJON.  175 

that  the  energy  transmitted  to  the  enclosure  by  the  radiating 
sphere  at  a  differential  temj)erature  of  16°  will  be  exactly 
balanced  by  the  energy  transmitted  by  the  pencil  of  rays  at 
64°  entering  through  the  perforation  of  the  enclosure,  the  area 
of  which  is  0.25  of  the  convex  area  of  the  sphere. 

The  demonstration  thus  presented,  it  will  be  admitted, 
establishes  the  important  fact  that  the  temjierature  produced 
by  solar  radiation  is  four  times  higher  than  the  differential 
temperature  of  a  black  sphere,  composed  of  materials  of  per- 
fect conductivity,  exposed  to  the  sun,  and  permitted  to  radiate 
freely  towards  an  enclosure  of  a  unifonn  temperature. 

Let  us  now  examine  the  instrument  before  referred  to, 
shown  by  out  illustiation,  which  represents  a  section  through 
the  central  vertical  plane :  I-  j9  is  a  spherical  vessel  com- 
posed of  copper,  charged  with  water  and  coated  with  lamp- 
black on  the  outside,  suspended  within  a  spherical  enclosure 
0.  The  latter  is  provided  with  a  circular  opening  a  h,  to 
which  a  cylindrical  tniuk  a  g  is  attached,  the  spherical  enclo- 
sure as  well  as  the  trunk  being  coated  with  lamp-black  on 
the  inside,  as  shown  by  the  black  tint  in  the  illustration. 
A  thermometer  provided  with  a  cylindiical  bulb  is  inserted 
into  the  spherical  vessel,  and  also  a  rotating  paddle-wheel, 
operated  by  an  axle  passing  through  a  water-tight  stuffing- 
box.  A  cylindrical  vessel  r  r,  filled  with  water,  surrounds 
the  spherical  enclosure  and  trunk,  nozzles  being  applied  at 
the  top  and  bottom,  to  which  flexible  tubes  are  attached  for 
circulating  a  cuiTent  of  cold  water  through  the  vessel.  The 
instrument  is  mounted  within  a  revolving  observatory,  and 


176  BADIANT  HEAT.  chap.  ix. 

attacLed  to  a  table  turning  on  horizontal  journals,  and  pro- 
vided witli  appropriate  meclianism,  by  means  of  wliicli  it 
may  be  directed  at  right  angles  to  the  sun.  It  mil  be  evi- 
dent that,  if  the  axis  of  the  cylindrical  trunk  a  g  be  pointed 
accurately  towards  the  centre  of  the  sun,  the  sphere  Tc  2>  will 
receive  the  whole  radiant  energy  of  the  rays  within  the  tan- 
gential lines  h  f  and  p  g,  the  sectional  area  of  the  pencil  of 
rays,  as  before  stated,  being  0.25  of  the  convex  area  of  the 
sphere.  It  will  be  evident  also  that,  owing  to  the  opening  a  l> 
of  the  spherical  enclosure,  the  sphere  h  p  will  not  be  acted 
upon  by  the  full  amount  of  refrigeration  that  would  be  pro- 
duced by  the  radiation  of  a  continuous  enclosure.  Agreeably 
to  the  theory  of  exchanges,  the  deficiency  will,  however,  not 
be  great,  since  the  side  /  «  of  the  tnink  a  g  will  radiate  as 
powerfully  towards  the  sphere  as  a  portion  of  the  spherical 
enclosure  corresponding  with  the  angular  distance  determined 
by  the  radial  lines  a  e  and  /  c.  But  the  convex  surface  of 
the  segment  e  d,  depending  on  the  angle  subtended  by  f^  c 
and  g  c,  will  obviously  be  subjected  to  far  less  refrigeration 
than  an  equal  surface  on  the  opposite  side  of  the  sphere. 
Regarding  the  exact  amount  of  deficient  refrigeration  conse- 
quent on  the  opening  in  the  enclosure  at  a  h  referred  to,  it 
will  be  perceived,  on  reflection,  that  the  radiation  of  the 
enclosure  towards  the  semi-spherical  surface  presented  to  the 
sun  will  be  reduced  in  the  exact  proportion  which  the  area 
e  d  bears  to  the  entire  convex  area  of  the  semi-sphere.  It 
will  be  seen,  therefore,  that  although  the  condition  coupled 
with   our   proposition   has   not  been   fully   complied   with — 


CHAP.  IX.        THE  FEEBLENESS  OF  SOLAli  RADIATION.  177 

namely,  that  tlie  enclosure  should  Le  of  great  extent  com- 
pared with  the  size  of  the  radiating  sphere— yet  the  enclo- 
sure of  our  instrument  and  the  comparatively  lai-ge  opening 
at  a  h  will  not  materially  aflfect  the  refrigerating  influence 
to  which  the  sphere  is  subjected.  Besides,  the  known  soliil 
angle  subtended  by  the  radial  lines  f  c  and  g  c  enable  us  to 
calculate  the  amount  of  deficient  radiating  surface  presented 
by  the  enclosure. 

Several  experiments  have  been  made  simultaneously  with 
tliis  instrument  and  a  standard  actinometer,  in  order  to  ascer- 
tain the  precise  relation  betAvecn  the  temperature  ti'ansmitted 
by  the  sun's  rays  to  the  radiating  sphere  and  to  the  actino- 
meter. Both  instruments  have  invariably  been  attached  to 
the  same  parallactic  table  during  the  investigation ;  conse- 
queiitly  the  energy  of  the  radiant  heat  transmitted  to  each 
has  been  precisely  alike.  Respecting  the  instituted  tests,  it 
will  suffice  to  record  the  result  of  an  experiment  conducted 
at  noon,  October  20,  1871,  the  solar  radiation  on  that  day 
being  of  nearly  average  intensity,  while  the  sun's  zenith  dis- 
tance, 51  deg.  40  min.,  was  also  near  an  average.  Observa- 
tions made  at  equal  intervals  of  5  min.,  from  11  hours  55 
min.  A.M.  to  12  hours  30  min.,  showed  that  the  radiating 
sphere  of  the  instrument,  the  contents  of  which  was  effec- 
tually agitated  by  the  internal  paddle-wheel,  attained  a  tem- 
perature of  precisely  75°,  while  the  enclosure  was  maintained 
at  a  constant  temperature  of  61°.3.  Accordingly,  an  increase 
of  temperature  of  13°.7  above  that  of  the  enclosure  was  pro- 
duced   by    the  solar  radiation    acting   freely    on    the    sphere, 


178  BADIANT  HEAT.  chap.  ix. 

the  actiuometer,  at  the  same  time,  indicating  a  temperature 

of  51°.36.     Now,  agreeably  to  our  theory,  the   temperature 

n     51.36 
of  the  sphere  ought  to  have  been  only  — - —  =  12  .84,  thus 

showing  a  discrepancy  of  13.7  -  12.84  =  0°.86  F.  It  has 
already  been  explained  that  the  sphere  does  not  receive  a 
full  amount  of  refrigeration,  in  consequence  of  the  opening 
in  the  enclosure  necessary  to  admit  the  cylindrical  trank ; 
hence  the  temperature  of  the  sphere  ought  to  exceed  that 
which  our  theory  has  established.  The  observed  difference, 
0°.86,  is,  however,  greater  than  it  should  be  in  accordance 
with  the  relative  magnitude  of  the  convex  surface  e  d  and 
the  area  of  the  sphere.  But,  referring  to  the  illustration,  it 
will  be  seen  that,  at  the  point  where  the  thermometer  is 
inserted,  a  considerable  area  of  the  sphere  is  not  subjected 
to  any  radiation  from  the  enclosure,  nor  at  the  point  where 
the  axle  of  the  paddle-wheel  enters.  Adding  these  areas  to 
that  of  e  d,  calculation  shows  that  the  amount  of  cold  radi- 
ation prevented  from  acting  on  the  sphere  accounts  very 
nearly  for  the  discrepancy  of  0°.86  F.  before  referred  to. 
We  are,  therefore,  warranted  in  stating  that  the  temperature 
indicated  by  the  actinometer  during  the  experiments  has 
j)roved  to  be  exactly  foiir  times  higher  than  that  indicated 
by  the  thermometer  inserted  in  the  sphere  exposed  to  the 
radiant  power  of  the  sun's  rays  and  to  the  refrigerating  in- 
fluence of  the  enclosure.  The  soundness  of  our  theory  has 
thus  been  fully  proved,  and,  consequently,  additional  evi- 
dence furnished  of  the  correctness  of   the   determination  of 


CHAP.  i.\.         THE  FEEBLENESS  OF  SOLAli  RADIATION.  179 

solar  intensity  by  means  of  the  actinomeiev  described  in 
Chap.  III.  No  further  proof  is  needed  in  support  of  the 
demonstration  already  presented,  sho^^ang  that  the  tempera- 
ture produced  by  solar  radiation,  instead  of  being,  as  Sir 
John  Herscliel  supposed,  equal  to  the  maximum  shade  tem- 
perature within  the  tropics  added  to  the  temperature  of  the 
Fahrenheit  zero  above  absolute  zero — viz.,  100  +  460  =  5G0° 
F. — scarcely  reaches  88°  F.  at  a  distance  of  91,430,000  miles 
from  the  solar  centre. 

Concerning  the  radiant  heat  which  reaches  the  distant 
planets  of  the  solar  system,  the  stated  discrepancy  is  of  vital 
importance.  Were  it  true  that  the  intensity  of  the  sun's 
radiant  heat  is  560°  F.  at  the  distance  mentioned,  the  rays 
on  reaching  Jupiter's  atmosphere  would  be  capable  of  de- 
veloping a  temperature  of  — — ^  =  20°.7   F.     We  can  readily 

imagine  that  the  atmosphere  of  the  giant  planet  might,  by 

some  system  of  accumulation,  raise  this  temperature  to  such 

a  degree  that  organisms  like  those  of  the  earth  might  be  sus- 

88 
tained.     But  can  the  insignificant  temperature  of  —  =  3°.2  F. 

transmitted  to  Jupiter's  atmosphere  be  sufficiently  elevated  by 
the  process  of  accumulation  to  sustain  animate  and  vegetable 
organizations  resembling  those  of  our  planet  ?  The  stated 
low  temperature  need  excite  no  sui-prise  if  we  reflect  on  the 
fact  that  the  sun,  as  seen  from  the  boundary  of  the  atmo- 
sphere of  Jupiter,  is  no  larger  thiin  an  orange  viewed  at  a 
distance  of  one  hundred  feet.     As  seen  from  Saturn,  the  size 


ISO  J?ADIANT  TIEAT.  CHAP.  ix. 

of  the  sun  is  that  of  a  musket-ball  at  a  distance  of  fifty  feet 
from  the  observers  eye ;  while  the  transmitted  solar  heat 
scarcely  develops  a  temperature  of  1°  F.  where  it  enters 
Saturn's  atmosphere.  Speculations  regarding  the  habitabi- 
lity  of  the  distant  planets  are  futile,  in  view  of  the  insuffi- 
cient radiant  intensity  of  solar  emission  established  by  the 
actinometric  observations  recorded  in  this  work,  and  by  the 
adopted  tests  proving  their  reliability. 


CHAPTER  X. 

TEMPERATURE  OF  THE  SOLAR  SURFACE. 


The  illustration  on  Plate  19  represents  an  instrument  for 
ascertaining  tlie  temperature  of  the  surface  of  the  sun.  At  first 
sight  it  Avill  appear  futile  to  undertake  the  construction  of  an 
instrument  capable  of  indicating  temperature  at  a  distance 
exceeding  90,000,000  miles ;  but  in  view  of  the  fact  that  the 
sun  has  been  weighed  by  an  instrument  consisting  principally 
of  four  leaden  balls  less  than  one  foot  in  diameter,  the  attemjjt 
cannot  justly  be  deemed  absurd.  The  reader  will  remember 
that  in  the  celebrated  Cavendish  experiments,  afterwards  re- 
peated by  Baily  and  others,  the  weight  of  the  earth — on 
which  the  weight  of  the  sun  is  based — was  ascertained  by 
measuring  the  attraction  exerted  by  spheres  of  lead  weigh- 
ing 174  lbs.  The  delicate  nature  of  the  experiment  may  be 
infen-ed  fi-om  the  fact  that  the  ascertained  attractive  force 
was  found  to  be  only  nVir  of  a  grain.  The  illustrated  instiu- 
ment,  the  solar  pyrometer,  by  means  of  which  the  tempei'atui'e 
of  the  sun  has  been  measured,  involves  no  such  nicety. 


181 


182  BABIANT  HEAT  chap.  x. 

Before  entering  on  a  description  of  the  solar  pyrometer, 
it  will  be  necessary  to  call  attention  to  tlie  demonstration  in 
Chap.  I.,  showing  that  the  law  relating  to  radiating  spheres 
is  also  applicable  to  concave  spherical  radiators,  if  the  sub- 
stances exposed  to  their  radiant  heat  be  placed  in  their  foci. 
The  demonstration  referred  to  also  proves  that  the  tempera- 
ture produced  by  the  radiant  heat  transmitted  by  concave 
radiators  of  equal  temperatures  and  curvature,  at  equal  dis- 
tances, is  directly  as  their  areas.  Melloni  and  Leslie's  experi- 
ments, conducted  in  the  presence  of  the  disturbing  influences 
of  atmosjjheric  air,  not  being  sufficiently  accurate  to  warrant 
their  being  cited  in  support  of  the  correctness  of  the  stated 
relation  between  areas  and  temperatures,  the  construction  of 
the  pyrometer  has  been  so  modified  as  to  enable  us  to  prove, 
independently  of  the  demonstrations  in  the  preceding  chapter 
referred  to,  that,  under  the  stated  conditions,  the  temperatures 
correspond  exactly  with  the  areas. 

Our  illustration  represents  a  longitudinal  section  through 
the  vertical  plane,  and  a  photographic  perspective  view  of  the 
pyi'ometer.  It  will  be  seen,  by  inspecting  the  longitudinal  sec- 
tion, that  the  instrument  is  composed  of  four  principal  parts : 
(1)  A  heater  consisting  of  a  cylindrical  vessel  with  spherical 
bottom  and  open  top,  supported  by  an  ordinary  stove,  the  fire- 
chamber  of  which  it  partially  entei's.  Enlargements  resem- 
bling truncated  cones  with  concave  spherical  ends  are  formed 
near  the  middle  of  the  heater.  The  latter  is  pai-tially  filled 
with  water,  as  shown  in  the  illustration.  (2)  A  conical  vessel, 
surrounded  by  a  double  casing,  secured  to  the  base  of  the 


CHAP.  X.  TEMPEHATUBE  of  the  SOLAB  SriiFACE.  183 

large  conical  enlargeiueut  of  the  heater.  (3)  A  cylindrical 
vessel  secured  to  the  small  end  of  the  enlai-gement,  likewise 
surrounded  by  a  double  casing.  (4)  An  ordinaiy  stove,  into 
wliicli  the  lower  end  of  the  heater  is  inserted.  The  curva- 
ture of  the  spherical  concavity  at  the  base  of  the  large  conical 
enlargement  of  the  heater  is  stioick  to  a  radius  of  18  inches, 
its  diameter  being  10  inches,  hence  presenting  an  area  of  78.84 
square  inches.  The  opposite  spherical  concavit}-,  the  ladius  of 
which  is  9  ins.  (its  diameter  being  5  ins.)  presents  an  area  of 

78.84 

— - —  =  19.51   square  inches.     Thermometers  are  applied  at 

the/(9Ci  of  the  spherical  concavities,  their  stems  being  placed 
as  shown  in  the  illustration,  in  order  that  the  bulbs  may 
present  unobstructed  semispheres  towards  the  radiatoi-s.  It 
is  hardly  necessary  to  observe  that  thermometers  intended  to 
measure  the  intensity  of  radiant  heat  should  be  protected  so 
that  those  parts  of  their  bulbs  which  are  not  acted  upon  by 
the  heat-rays  emanating  from  the  radiators  may  not  lose  their 
heat  by  radiation  or  convection.  The  cylindrical  as  well  as 
the  conical  chamber  of  the  pyrometer  containing  the  ther- 
mometers are  connected  by  suitable  tubes  with  an  air-pump, 
by  which  the  air  is  withdrawn ;  a  current  of  water  being 
circulated  through  the  double  casings  when  the  instrument 
is  in  operation.  With  reference  to  the  heater,  it  should  be 
observed  that,  being  open  at  the  top,  the  water  it  contains 
will  always  be  maintained  at  a  constant  temperature  when 
the  furnace  is  in  action. 

It  ma}-  be  briefly  stated  that  the  principle  of  the  pyro- 


1S4  BADIANT  HEAT.  chap.  x. 

meter  is  tliat  of  ascertaiiiiiig  solar  intensity  by  comparing 
tlie  temperature  transmitted  liy  a  concave  spherical  radiator 
(if  10  ins.  diameter  to  a  tliermometer  placed  at  a  distance 
of  IS  ins.  from  its  face,  ■\^itll  tlie  temjjerature  produced  by 
the  radiant  Leat  emanating  from  an  incandescent  sphere  of 
832,584  miles  in  diameter,  at  a  distance  of  91,430,000  miles. 
The  radiant  heat  in  both  cases  is  transmitted  through  ether; 
in  the  former  to  the  sui-face  of  the  bulb  of  the  enclosed  ther- 
mometer ;  in  the  latter  to  the  boundary  of  the  earth's  atmo- 
sphere. The  law  which  governs  the  transmission  of  radiant 
heat  through  space  is  as  absolute  as  the  law  of  gravitation, 
whatever  be  the  distance ;  hence  it  is  indisputable  that  the 
solar  pyrometer  in  which  the  radiant  heat  acts  at  a  distance 
of  18  inches  is  as  competent  to  determine  the  temperature 
of  the  sun  as  the  Cavendish  leaden  spheres  acting  at  a  dis- 
tance of  8.85  inches  to  determine  his  weight.  The  chances, 
however,  of  an  exact  determination  are  greatly  in  favor  of 
the  pyrometer.  In  the  first  place,  while  the  area  of  the  con- 
cave radiator  of  the  j^yrometer  is  to  the  area  of  the  great 
circle  of  the  sun  as  1  :  2,871  X  10",  the  weight  of  the  leaden 
ball  employed  in  the  Cavendish  experiments  is  to  the  weight 
of  the  sun  as  1  :  2,367  X  10";  thus  showing  a  difference  of 
1  :  824,500,000  in  favor  of  the  pyrometer.  Besides,  the  ele- 
ment of  distance  through  which  the  radiant  and  the  gravi- 
tating forces  act  is  in  favor  of  the  pyrometer,  in  the  ratio  of 
18  to  8.85.  But  these  considerations,  however  important  on 
account  of  the  greater  difference  of  the  magnitudes  involved, 
may  be  considered  unimportant  in  comparison  with  the  direct- 


CUAI>.  X.  TEMPJiKATUIiE  Of  THE  HOLAU  HUEFAVE.  185 

ness  of  the  means  by  Avliich  the  solar  pyrometer  solves  the 
problem,  contrasted  with  the  indirectness,  exceeding  compli- 
cation, and  nicety  involved  in  the  Cavendish  experiments. 
In  the  solar  pyrometer  we  only  require  a  correct  indication 
of  the  tempeiature  of  the  radiating  concave  spherical  surface, 
and  of  the  temperature  transmitted  to  its  focus ;  together 
with  au  accurate  measurement  of  the  distance  of  that  focus, 
and  of  the  area  of  the  radiating  suiface.  These  points  being 
readily  determined,  while  the  relative  distance  and  diameter 
of  the  sun  and  the  temperature  produced  by  solar  radiation 
at  the  boundary  of  the  terrestrial  atmosphere  are  known,  we 
may  enter  upon  and  carry  out  our  computation  without  intro- 
ducing a  single  correction.  How  different  the  Cavendish  expe- 
riment, with  its  nimierous  disturbing  elements  depending  on 
barometric  and  thermometric  conditions  and  changes,  influenc- 
ing a  gravitating  force  amoimting  to  only  rAir  of  a  grain  ! 
An  account  of  the  almost  insuperable  difliculties  which  were 
surmounted  in  those  remarkable  experiments,  which  for  inge- 
nuity, care,  and  perseverance  stand  unequalled  in  the  annals 
of  physics,  would  be  out  of  place  here  ;  yet  the  foregoing 
brief  allusion  to  experiments  which  satistactorily  determined 
the  weight  of  the  earth,  and  thereby  the  weight  of  the  sun, 
has  been  deemed  appropriate  as  a  contrast.  The  dii-ectness, 
facility,  and  cei-tainty  of  measuring  solar  temperature  by  the 
means  we  are  now  considering  A\oixld  scarcely  be  appreciated 
without  calling  to  mind  the  method  adopted  for  ascei-taining 
the  sun's  weight. 

Referring  to  the  construction  of  the  solar  pyrometer  and  its 


186  JiABIANT  HEAT.  CHAP.  X. 

apparently  ponderous  cliaractei',  it  Avill  be  ^\  ell  to  bear  in  niiml 
tliat  tlie  indispensable  condition  in  this  instrument  of  maintain- 
ing a  constant  temperature  of  the  couipHratively  large  con- 
cave spherical  radiator  is  not  easily  fullilled.  Kotliing  short 
of  an  o^yen  heater  containing  a  fluid  Avhich  readily  evaporates, 
and  the  application  of  an  excess  of  heating  power,  will  effec- 
tually accomjUish  the  object  in  view.  Evidently  the  loss 
occasioned  by  radiation  cannot  be  exactly  made  good  by  the 
most  delicate  mechanical  contrivance ;  but  by  applying  an 
excess  of  heat  in  the  furnace,  the  fluid  which  regulates  the 
temperature  of  the  radiator  will  be  prevented  from  falling 
below  the  boiling  point ;  and  since  the  heater  is  open,  the 
steam  formed  will  caiiy  off  superfluous  heat,  and  thus  main- 
tain the  fluid  at  the  desired  unifoi'm  temperature.  The 
exhaiisted  chambers  which  contain  the  thei'mometers  must 
of  course  be  maintained  at  a  constant  temperature,  the  least 
fluctuation  being  fatal  to  accurate  indication  of  the  intensity 
of  the  heat  transmitted  by  the  radiators.  In  order,  there- 
fore, to  keep  up  the  necessaiy  constant  temperatui'e  during 
the  investigation,  a  current  of  water  has  been  circulated 
throuo-h  the  double  casinos  which  surround  the  exhausted 
chambers.  By  this  expedient,  in  connection  with  the  per- 
fectly uniform  temperatui'e  maintained  in  the  heatei',  it  has 
been  easy  to  ascertain  with  critical  nicety  the  temperature 
produced  by  the  radiant  heat  transmitted  from  the  spherical 
radiator  to  its  focus.  Eegarding  the  area  and  curvature  of 
the  radiators,  accurate  workmanship  alone  will  insure  A\hat 
is  requisite ;  but  the  position  t>f  the  thermometei',  the  placing 


CHAP.  X.       TEMrEnATrin-:  or  tiik  solar  srnFACE.  isr 

the  bull)  at  tlie  proper  distance  with  reference  to  the  focus, 
demands  some  consideration.  Obviously  it  would  not  be 
correct  to  place  the  centre  of  the  bulb  in  the  focus  of  the 
radiator,  as  that  would  bring  the  face  of  a  bulb  of  i  in. 
diameter  ^  in.  in  ailvance  of  said  focus  ;  nor  would  it  be 
proper  to  carry  the  bulb  so  far  back  that  its  face  would 
intei"sect  the  focus.  The  focal  distance  being  18  ins.,  it  will 
be  found  that  placing  the  bulb  half  way  between  these  two 
positions  will  cause  an  error  of  fully  0.007.  Conflicting  indi- 
cation, it  should  be  oliserved,  is  unavoidable,  since  every  part 
of  the  exposed  half  of  the  convex  surface  of  the  bulb  can- 
not be  equidistant  from  the  face  of  the  concave  i-adiator ; 
but  this  notwithstanding,  there  is  a  distance  at  which  the 
indication  of  the  thermometer  will  be  precisely  the  same  as 
if  its  entire  contents  were  concentrated  in  the  focus  of  the 
radiators.     This  position  has  been  practically  determined. 

The  hitherto  accepted  doctrine,  that  the  intensity  of  radi- 
ant heat  is  directly  as  the  area  of  the  radiatoi-s,  for  equal 
distances,  has  been  shoA\n,  in  a  previous  chapter,  to  be  fal- 
lacious, because  the  radiant  heat  transmitted  from  the  boun- 
daries of  plane  radiators  becomes  enfeebled  by  distance  and 
the  conserpient  dispersion  of  the  heat-rays,  in  the  ratio  of 
the  squares  of  the  distance  between  the  I'adiator  and  the 
recipient  of  the  radiant  heat.  The  solar  pyi-ometer  having 
been  constrnctetl  before  I  had  satisfactorily  demonstrated 
that  the  intensity  of  the  radiant  heat  transmitted  from  con- 
cave spherical  surfaces  is  directly  as  the  areas  of  such  ladi- 
ators,   it  was  deemed    necessary  to  esta1)lish   the  correctness 


188  BADIANT  HEAT.  chap.  x. 

of  that  assumption ;  hence  the  solar  pyrometer  has  been 
modified  as  before  mentioned.  The  lesser  radiator  attached 
to  the  conical  enlargement  of  the  heater,  and  the  cylindrical 
chamber  enclosing  the  same,  were  accordingly  added  to  the 
instrument.  It  has  already  been  stated  that  the  area  of  the 
spherical  radiatoi'  within  the  conical  chamber  is  exactly  four 
times  greater  than  that  of  the  opposite  radiator,  and  that  the 
radius  of  the  curvature  of  the  latter  is  one-half  of  the  radius  of 
the  former.  The  demonstration  contained  in  Chap.  I.,  before 
referred  to,  has  established  the  fact  that  in  concave  sphe- 
rical radiators  presenting  equal  areas  the  radiant  heat  trans- 
mitted is  in  the  inverse  ratio  of  the  square  of  the  distances 
if  the  substance  exposed  to  the  radiant  heat  be  placed  in 
the  focus  of  the  radiator.  It  follows  from  this  demonstra- 
tion that,  for  equal  area,  the  intensity  of  the  radiant  heat 
transmitted  to  the  focus  of  the  lesser  radiator  will  be  four 
times  greater  than  the  intensity  of  the  radiant  heat  trans- 
mitted to  the  focus  of  the  large  radiator.  But  the  area  of 
the  latter  is  exactly  four  times  greater  than  the  area  of  the 
former,  while  the  thermometers  in  both  chambers  are  exposed 
to  the  radiation  of  surfaces  heated  by  the  same  medium,  and 
therefore  of  precisely  equal  temperatures.  At  the  same  time 
these  thermometers  ividiate  against  surfaces  maintained  at  a 
constant  temperature,  by  the  reliable  expedient  of  employ- 
ing a  powerful  continuous  current  of  water.  Consequently, 
the  enclosed  thermometers,  although  exposed  to  radiators  of 
different  area,  should  indicate  precisely  equal  temperature. 
Actual  trial  having  shown  that  such  is  the  case,  the  correct- 


CHAP.  X.         TEMPEEATUBE  OF  THE  SOLAR  SUIiFACE.  180 

ness  of  the  foregoing  assumption  must  be  accepted  as  fully 
established. 

I  will  now  biieriy  advert  to  the  result  of  an  experiment 
made  with  the  solar  pyrometer  while  the  atmospheric  pres- 
sure balanced  29.91  inches  column  of  mercury,  the  tem- 
perature of  the  water  in  the  heater  being  then  precisely 
212°.  Apart  from  having  thus  insured  a  definite  indication 
of  heat  applied  to  the  concave  radiatoi-,  the  temperature  of 
the  current  of  cold  water  circulated  throuu-h  the  casinir  ■'^ur- 
rounding  the  exhausted  chaml>ers  did  not  fluctuate  in  the 
least  during  the  experiment,  the  thernionieter  inserted  in  the 
exit-pipe  of  the  casings  continuing  to  indicate  steadily  48°.l 
F.  The  circulation  of  cold  water  having  been  kept  up  fully 
half  an  hour  previous  to  the  experiment,  it  is  hardly  neces- 
sary to  state  that,  before  the  fire  ^\■as  applied  in  the  furnace, 
the  enclosed  thermometer,  the  surrounding  chamber,  the  watei- 
contained  in  the  heater,  and  the  radiator  all  indicated  48°.  1. 
The  fuel  in  the  furnace  having  been  ignited,  and  the  water 
in  the  heater  brought  to  boiling-point,  the  temperature  X)f 
the  spherical  radiator  was  observed  to  increase  from  48°.  1 
to  212°,  difference  =  163°.9  ;  the  temperature  of  the  focal 
thermometer  at  the  same  time  rising  from  48°.  1  to  G0°.3, 
difference  =  12°.2. 

It  results,  from  previous  demonstrations  (see  Chap.  I.), 
that  the  temperature  of  spherical  radiatin-s  transmitting  e(iual 
intensities  to  their  foci  are  invereely  as  the  square  of  the 
sines  of  half  of  the  angles  which  they  subtend — that  is,  the 
angles  formed  by  the  axis  of  the  radiator  and   the  heat-rays 


190  BADIANT  HEAT.  cuxv.  x. 

projected  from  tlie  oireiinifereiice  to  the  focus.  Conseqiiently, 
as  the  spherical  radiator  of  the  solar  pyrometer,  the  differen- 
tial temperature  of  which  is  163°.9,  transmits  to  its  focus  an 
intensity  of  12°.2,  -we  are  enabled  to  calculate  what  tem23e- 
I'ature  the  sun  must  possess  in  order  to  transmit  an  intensity 
of  12°.2  to  the  boundary  of  our  atmosphere.  The  mean  angle 
subtended  by  the  sun  being  32  min.  1  sec.  during  the  expe- 
riment, while  that  subtended  by  the  radiator  of  the  pyi'ometer 
was  32  deg.  15  min.,  it  follows  that  the  ratio  of  the  square 
of  the  sines  of  half  these  angles  will  be  1  :  3,567.7.  Accord- 
ingly, the  sun,  in  order  to  produce  by  its  radiant  heat  a  tem- 
perature of  12°.2  at  the  boundary  of  the  atmosphere  of  the 
earth,  must  possess  a  temperature  3,567.7  times  greater  than 
that  of  the  sjiherical  radiator  of  the  pyrometer.  This  latter 
temperature  being  163°.9,  that  of  the  sun  cannot  be  less  than 
3,567.7  X  163.9  =  584,746°  in  order  to  transmit  an  intensity 
corresponding  ^\ith  a  thermometric  interval  of  12°.2  on  the 
Fahrenheit  scale.  But  solar  intensity  at  the  boundary  of  our 
atmosjDhere,  as  shown  by  our  actinometric  observations   (see 

S4  S4 
Chap.  III.),  is  84°.84  ;  hence  —^ —  =  6.95  times  greater  than 

that  transmitted  by  the  radiator  of  the  pyrometer  to  its  focus. 
The  temperature  of  the  sun,  therefore,  cannot  be  less  than 
6.95  X  584,746  =  4,063,984  deg.  Fah. 

It  will  be  recollected  that  the  demonstration  in  a  preced- 
ing chapter  established  with  as  much  certainty  as  any  propo- 
sition in  the  "Principia"  that  the  temperature  produced  by 
the  radiant  heat  transmitted  l)y  a  sphere  of  uniform  tempe- 


•-•UAP.  X.        TEMrEUATUIiE  OF  TUE  tiVLAU  HUliFACE.  I'-'l 

ratiire  at  tlie  sui-fufe  is  to  the  teuipeniture  of  tlie  splieie 
itself  inversely  as  the  si|Uaie  of  the  ladiiis  to  the  square 
of  the  distance  fioni  the  centre  to  the  point  exposed  to  the 
radiant  heat.  The  distance  between  the  earth  and  the  sun, 
at  the  snnnuer  solstice,  being  such  that  the  angle  subtended 
by  the  latter  is  31  niiu.  32  sees.,  the  ratio  of  distance  and 
radius  will  l)e  218.1  :  1  ;  hence  the  ratio  of  the  squares, 
47,5G7  :  1.  Consequently,  the  temperature  of  the  sun  must 
be  47,507  times  greater  than  the  temperature  produced  by 
solar  radiation  at  the  boundary  of  the  earth's  atmosphere. 
That  temperature  being,  as  before  stated,  S4°.84,  the  sun's 
temperature  cannot  be  less  than  47,507  X  84°.84  =  4,035,584 
deg.  Fah.  Thus  the  previously  demonstrated  temperature  of 
4,063,984  deg.  Fah.,  based  on  the  indications  of  the  solar 
pyrometer  and  the  angles  subtended  by  its  radiator,  ditl'ers 
only  0.007  from  the  computations  just  presented.  The 
methods  by  means  of  which  these  results  have  been  reached 
diftering  entirely,  both  being  based  on  sound  physical  and 
mathematical  principles,  we  cannot  doubt  the  correctness  of 
the  determination.  Nor  can  it  be  questioned  that  the  actual 
temperature  of  the  surface  of  the  sun,  at  the  point  of  maxi- 
mum intensity,  is  still  higher,  since  the  lays  in  passing 
through  the  solar  atmosphere  suffer  considerable  loss  of 
energy,  as  shoA\n  in  Chap.  VI. 

Let  us  now  consider  briefly  the  extraordinary  diversity 
of  views  entertained  by  scientists  regarding  the  temperature 
of  the  sun.  In  view  of  the  fact  that  all  practical  data 
necessary  to  solve  the   problem  are   known,   it    is   sur[irising 


193  BABIANT  HEAT.  CHAP.  X. 

that  any  diflference  of  opiuiou  sliould  exist  on  the  subject. 
Zolluer  apparently  rejects  the  positive  evidence  of  high 
sohir  temperature  furnished  by  the  fact  that  the  sun's  rays, 
after  having  suffered  dispersion  in  the  ratio  of  4G,000  to  1, 
and  penetrated  the  terrestrial  atmosphere,  are  capable  of 
developing  a  temperature  of  nearly  70°  F.  on  the  ecliptic. 
It  will  be  remembered  that  he  published,  some  time  ago, 
an  elaborate  demonstration,  founded  on  the  height  of  the 
solar  prominences,  showing  that  the  sun's  temperature  does 
not  exceed  70,000°  C.  Secchi,  on  the  other  hand,  asserted, 
in  his  original  work  on  the  sun,  that,  owing  to  the  acces- 
sion of  energy  received  by  radiation  from  the  outer  layers 
of  the  solar  atmosphere,  the  temperature  of  the  surface  of 
the  photosphere  is  fully  140  times  gi-eater  than  the  tempe- 
rature announced  by  Zollner.  Let  us  first  notice  the  investi- 
gations of  the  Italian  astronomer.  In  his  work  "  Le  Soleil," 
published  at  Paris,  1870,  he  presents  calculations  showing  that 
the  temperature  of  the  solar  surface  is  at  least  10,000,000°  C. 
Prof.  Newcomb,  in  a  review  of  the  M'ork  referred  to,  pub- 
lished in  Nature,  showed  that,  if  the  temperature  reached 
ten  million  degrees  of  Centigrade,  as  asserted  by  the  author 
of  "Le  Soleil,"  the  earth  would  speedily  be  converted  into 
vapor.  In  ansAver  to  this  objection,  Pere  Secchi  urged,  "  that 
a  body  may  have  a  veiy  high  temperature  and  yet  radiate 
very  little,"  contending  "that  a  thermometer  dipped  inside 
the  solar  envelope  in  contact  with  the  photosphere"  would 
indicate  the  temperature  mentioned.  "  This  high  tempera- 
ture," he  observes,   "  is  really  a  virtual  temperature,  as  it  is 


CHAP.  x.         TEMPEliATUliE  OF  THE  soLM;  nUliFAGE.  103 

the  amount  of  radiation  received  from  all  the  transparent 
strata  of  the  sohir  envelope,  and  this  body  at  the  outer 
shell  must  certainly  be  at  a  lower  temperature."  What 
information  is  intended  to  be  conveyed  by  the  statement 
that  10,000,000"  C.  "is  really  a  virtual  temperature,"  on  the 
ground  that  it  is  "  the  amount  of  radiatiou  received  from  all 
the  transparent  strata  outside  of  the  photosphere,"  we  can 
only  conjecture. 

Our  demonstrations,  based  on  the  indication  of  the  solar 
pyrometei-,  ha\e  shown  that  the  supjjosed  thermometer,  if 
brought  in  contact  with  the  photosphere,  cannot  possibly 
indicate  the  enormous  temperature  of  10,000,000°  C.  assumed 
by  the  Italian  plnsicist.  The  assertion  that  "  a  body  may 
have  a  very  high  temperature  and  }et  radiate  but  very 
little,"  were  it  correct  with  reference  to  the  photosphere, 
does  not  aflect  the  question.  It  is  of  no  consequence  whe- 
ther the  photosphere  belongs  to  the  class  of  active  or  slug- 
gish incandescent  radiators  imagined  by  the  distinguished 
savant;  the  temperature  of  the  radiant  surface,  not  its  capa- 
city to  radiate  more  or  less  copiously,  is  the  problem  to  be 
solved. 

Very  recently  Pere  Seechi,  much  to  the  surprise  of  those 
who  had  accepted  his  estimate  of  solar  temperatui-e  published 
in  "  Le  Soleil,"  has  changed  his  views  completely.  In  an  ela- 
borate essay  presented  to  the  Academy  of  Sciences  at  Paris 
he  underrates  the  intensity  of  solar  energy  more  than  he  for- 
merly overestimated  it.  Apprehensive  that  a  synopsis  would 
fail   to  give  a   correct   idea  oi  the   rcmarkalde   demonstration 


194  BADIANT  HEAT.  CHAP.  X. 

by  wliicli  tlie  author  of  "  Le  Soleil "  now  reverses  all  his 
previous  notions  on  the  subject,  and  in  order  to  furnish  a 
complete  exposition  of  the  untenable  character  of  the  hypo- 
thesis tending  to  discredit  the  result  of  my  labors,  I  will 
present  without  abridgment  the  essential  points  of  his  com- 
munication to  the  French  Academy,  jjublished  in  "  Comptes 
Eendus,"  Tome  LXXVIII.,  No.  11  :  "  During  last  summer 
(1873)  I  made  some  experiments  in  order  to  determine  the 
relation  of  the  radiation  of  the  sun  to  that  of  the  electric 
light,  in  the  hope  of  solving  the  question  of  solar  tempera- 
ture. This  source  of  light  was  selected,  because  its  inten- 
sity differs  the  least  from  that  of  the  sun.  Hence  I  expect 
to  harmonize  the  conflicting  opinions  regarding  the  law  of 
radiation  existing  among  the  followers  of  Kewton  and  those 
of  Dulong  and  Petit.  In  estimating  the  t^vo  radiations  I  have 
used  the  thernioheliometre,  the  same  apparatus  described  in 
my  work  '  Le  Soleil.'  This  instrument,  in  spite  of  the  objec- 
tions made  to  it  [by  the  wiiter  of  this  work],  seems  to  me 
appropriate,  particularly  for  determining  mere  diiferences,  as 
in  this  case.  Let  I^  and  I,,  be  the  absolute  intensities  of 
the  radiations  of  the  sun  and  of  the  charcoal  points ;  0,  and 
Be  the  excess  of  temperature  of  the  black  thermometer  above 
that  of  the  surrounding  medium,  in  the  cases  of  the  solar  and 
the  electric  radiations ;  a  and  6  the  apparent  diameters  of  the 
radiating  surfaces,  viewed  from  the  centre  of  the  black  thermo- 

d,       I,  tang.'  6  6,  tang.'  a 

meter,  and  we  have  —  =  ~ ^^^  whence  1,  =  1^  -— rz  • 

'  d^       I,  tang.-  a  t^c.  tang.   6 

It   is   very    difficult    to    determine    practically    the    radiating 


CHAP.  X.  TEMrERATUliK  OF  TlIK  SOLA  I;  SURFACE.  105 

surface  of  the  charcoal  points.  The  point  is  generally  very 
lirilliant,  but  beyond  this  the  incandescence  decreases  very 
lapidly;  besides,  the  arc  between  them  has  a  very  different 
I'adiation.  We  have  tried  to  determine  the  sui-face  of  the 
radiating  parts  of  the  charcoal  points  1iy  comparing  their 
dimensions  with  those  of  glass  tul)es  placed  in  their  imme- 
diate vicinity,  and  estimating  the  distance  at  which  a  thin 
wire  of  platinum  commenced  to  melt  without  touching  tliera. 
We  have  thus  obtained  an  almost  rectangular  surface,  equal 
to  that  of  a  circle  of  1  centimetre  in  diameter;  besides,  the 
radiation  from  the  parts  outside  of  this  limit  was  intercepted 
by  diaphragms.  The  pile  consisted  of  50  elements  (Bunseu) 
immersed  in  fresh  nitric  acid.  The  diameter  of  the  ele- 
ments was  n".12  and  their  height  (i°.20.  The  electrodes  were 
short  and  very  tliii-k  ;  the  current  was  so  intense  that  the 
insulating  plates  of  an  apparatus  of  Foucault  were  fused 
almost  immediately,  and  an  iron  wire  of  1  millimetre  in  dia- 
meter and  2".50  of  length  \vas  constantly  kept  at  "white- 
heat."  The  author  having  explained  that  these  data  are 
vague,  proceeds :  "  Having  placed  the  thermoheliometre  at 
a  level  with  the  charcoal  points  and  the  black  thermometer 
at  a  distance  of  0".395,  I  found  after  half  an  hour  a  dif- 
ference of  3°.03  between  the  temperature  of  the  surrounding 
medium  and  the  lilack  thermometer.  During  sevei'al  days  of 
July,  about  noon,  I  determined,  with  the  same  instrument, 
the  temperature  produced  by  solar  radiation.  I  found  a  dif- 
ference of  IT^.ST,  allowing  for  zenith  distance.  By  sul)stitut- 
ing   these  amounts  in   the  previous  fornuda   and   calcidatiug 


196  BADIANT  HEAT.  CHAP.  X. 

the  diameters  a  and  d  according  to  the  dimensions  and  dis- 
tances of  the  radiating  atmosphere,  ^ve  ha^■e  I,  =  I^  X  36.468, 
making  the  intensity  of  solar  radiation  ;36A  times  greater  than 
that  of  the  charcoal  points.  This  estimate,  however,  falls 
short  of  the  actual  temperature  ;  for  we  know  that  the  cor- 
rection for  atmosjiheric  absorption  is  too  small.  Mr.  Soret 
has  found  on  the  Mont  Blanc  21°.18  ;  at  the  upper  limit  of 
our  atmosphere  that  amount  would  probably  be  about  27°. 
These  two  amounts  would  give  respectively :  For  21°.13  :  I^ 
=  I„  X  44.36 ;  for  27°.00 :   I,  =  I,  X  56.66. 

These  results  differ  materially  from  those  obtained  by 
other  observers.  Apj^rehending  that  some  unknown  cause  in 
my  electi'ic  light  might  produce  an  excessive  error,  I  com- 
jjared  it  with  the  light  from  a  stearin  candle.  I  found  that 
it  equalled  1,450  common  candles,  showing  the  intensity  of 
an  ordinary  good  pile.  In  another  series  of  expei'iments,  in- 
stituted when  the  pile  had  worked  for  some  time,  I  found 
Ij  =  lo  X  47.5,  Avhich  result  differs  very  little  from  that 
obtained  by  adopting  the  temperature  of  21°.  13  observed  by 
Mr.  Soret.  Thus,  if  we  accept  this  temperature  of  21°.  13, 
which  is  incontestably  below  the  real  one,  and  supposing  the 
temperature  of  the  radiating  surface  of  the  charcoal  points  to 
be  3,000° — an  amount  by  no  means  exaggerated,  since  that 
]5art  of  the  platin^un  exposed  to  the  heat  was  fused — and  if 
we  estimate  radiation  as  proportional  to  temperature,  \ve 
obtain  133,780°  as  the  potential  temperature  of  the  sun. 
This  amount  may  be  raised  even  to  169,980°,  by  adopting 
the  temperature  of  27°  produced  by  solar  radiation." 


CHAP.  X.         TEMPEBATUIiE  OF  THE  SOLAR  SURFACE.  197 

The  result,  then,  of  Pore  Seechi's  Latest  researches  shows 

that  the  potential  temperature  of  the  sun  is  1;{3,78U'  C,  which 

he  thinks  may  l)e  raised  even  to    169,980°  C.     Accordingly, 

,  .     ,  .  ,      ,       .  .  10,000,000°  C. 

Ills  loriiier  coiniJiitatitin   ot  solar  inteiisitv  was   

'■  ■  169,980"  C. 

=  59  times  hii^du'r  than  his  jiresent.  Referring  to  Chap. 
XIII.,  it  will  lie  found  that  I'diiillet,  whose  estimate  of  solar 
intensity  at  the  boundary  of  the  terrestrial  atmosphere  is 
nearly  identical  with  that  which  my  actinometric  observa- 
tions have  established,  but  who  bases  his  computations  on 
Duloiig  and  Petit's  erroneous  formula,  arrives  at  the  con- 
clusion that  the  temperature  of  the  sun  is  from  1,461°  to 
1,761°  C.  (mean  =  1,611°  C.)  M.  Vicaire,  adopting,  like 
Pouillet,  Dulong's  law,  states,  in  his  paper  presented  to  the 
Preiich  Academy,  that  the  temperature  deduced  from  that 
law  is  between  1,400°  and  1,500°  C.  Sainte-Claire-Deville 
concludes  his  essay  on  solar  temperature  by  the  announce- 
ment that  "  solar  temperature  will  not  lie  found  far  removed 
from  2,500°  to  2,800°  C."  It  is  very  important  to  observe 
that  no  difference  of  opinion  exists  regarding  the  fh/uatuic 
inevfjij  developed  by  the  sun.  All  physicists  accept  Pouillet's 
computation  showing  that  each  square  foot  of  the  solar  sur- 
face develops  about  300,000  thermal  units  per  minute.  It  will 
be  asked  ho\v  Pouillet  could  reconcile  such  an  eiu)rmous  deve- 
lopment of  energy  with  the  insignificant  intensity  represented 
by  1,611°  C.  A  satisfactory  answer  will  be  found  in  Chap.  II. 
An  examination  of  ^Ir.  Poxc's  tabic  of  temperatures  in  Chap. 
XIII.    will    also   suggest    a   satisfactory   answer.     This    table 


lOR  FABFANT  HEAT.  chap.  x. 

slioAvs  that,  agreeal)ly  to  Diiloiig's  foi'imila,  the  radiant  energy 
of  a  body  raised  to  a  temperature  of  2,520°  F.  is  4,600  times 
greater  than  the  radiant  energy  developed  by  a  body  raised 
to  a  temjDerature  of  60°  F.  above  that  of  the  atmosphere.  It 
is  needless  to  enter  into  any  further  discussion  showing  that 
the  low  solar  temperature,  1,611°  C,  assumed  by  Pouillet, 
results  from  the  adoption  of  the  enormous  emissive  power 
of  radiators  announced  by  Dulong  and  Petit.  It  should  be 
borne  in  mind  that  no  peculiar  property  has  been  attributed 
to  solar  radiation,  by  Pouillet  or  other  scientists,  distinguish- 
ing it  from  the  radiation  of  such  metallic  substances  as  those 
on  which  Dulong  and  Petit  experimented.  Consequently,  if 
we  can  show  l)y  j^i'actical  test  that  the  radiation  of  fluid 
metals  raised  to  a  temperature  of  1,611°  C.  develops  only  a 
small  fraction  of  the  energy  assigned  by  Dulong's  formula 
to  that  temperature,  we  prove  conclusively  that  the  method 
is  fallacious  Avhich  Pouillet  and  others  have  adopted  in  deter- 
mining the  temperatui'e  of  the  solar  surface.  Now,  the  result 
of  the  calorimetric  measurement  of  the  radiant  energy  of  fused 
and  overheated  iron,  recorded  in  Chap.  XIII.,  has  established 
in  the  most  positive  manner  that  the  emissive  power  at  a 
temperature  of  3,000°  -  60  =  2,940°  F.  (1,633°  C.)  above  that 
of  the  atmosphere  amounts  to  only  1,013  thermal  units  per 
minute  upon  an  area  of  one  square  foot.  Pouillet's  notions 
of  solar  emission  being  based  on  the  assumption  that  a  tem- 
perature of  1,011°  C.  is  capable  of  developing  300,000  thermal 
units,  while  actual  trial  shows  that  only  1,013  units  are  deve- 
loped by  the  radiation  of  fused  metal   at  even  a  liigher  tem- 


OHAI'.  X.  TEMrKRATUliE  OF  I'UE  HOLAU  HVRFAL'E.  I'.iO 

pfiature,  we   are   compelled  to  reject  liis   estiiuato   of   st>lar 
temperature  as  wholly  erroneous. 

It  sliould  be  observed  that  our  precise  determinatitiu  of 
solar  energy  by  means  of  the  calorimeter  descriljed  in  C'liap. 
V.  shows  that  322,000  thermal  units  are  developed  in  una 
minute  by  each  square  foot  of  the  solar  surface.  Notwith- 
standing this  enormous  development  of  dynamic  energy,  the 
emissive  power  of  the  sun  is  relatively  less  than  that  of 
fused  cast  iron  ;  a  fact  which  tends  to  prove  that  the  sun's 
radiant  heat  emanates  from  incandescent  gases.  A  brief  ana- 
lysis of  this  important  matter  will  be  appropriate  in  tliis 
place.  The  radiant  energy  or  emissive  power  developed  by 
the  sun  being  322,000  thermal  units  per  minute  upon  each 
square  foot  of  surface,  while  boiling  iron  at  a  temperature 
of  2,940°  F.  develops  1,013  units  upon  one  square  foot, 
during   one   minute,   it   follows   that   the   emissive  power   of 

322  000 

the   sun   is   only   '- =  318  times  greater  than  that  of 

•'      1,013 

iron  at  the  stated  temperature.     But  the  temperature  of  the 

.    4,030,000 
solar  surface  being  at  least  4,036,000°,  its  intensity  is      ^ 

=  1,373   times  greater  than  that  of  boiling  iron.     Sir  Isaac 

Newton  supposed  it  to  be  2,000  times  greater  than  that  of 

red-hot  iron ;    a  i-emarkable  agreement.     The  emissive  power 

1,373 
of  frised  iron  is  consequently  =  4.3  .tmies  greater  tlian 

318 

that  of  the  solar  surface  at  equal  temperature.     Now,  there  is 

no  terrestrial  incandescent  substance,  whether  solid  or  liquid. 


200  BADIANT  HEAT.  CHAP.  X. 

whose  emissive  power  is  not  more  than  oiie-fourtli  of  that  of 
iron  at  oorrespoiicling  temperatures  ;  lieiiee  it  is  reasonable  to 
infer  that  solar  radiation  emanates  from  incandescent  gases. 

Tlie  question  of  relative  radiant  power  of  solids  and  gases 
having  presented  itself  at  the  beginning  of  my  investigations 
of  radiant  heat,  I  constructed  the  apparatus  illustrated  on 
Plate  20,  in  order  to  ascertain  the  temperature  produced  by 
the  i-adiatiou  of  incandescent  gases.  The  illustration  repre- 
sents two  vertical  sections  of  the  apparatus  (see  Figs.  2  and  3) 
and  a  perspective  view  (see  Fig,  1).  Before  entering  on  a 
description,  it  will  be  proper  to  state  that  the  device  resorted 
to  was  intended  to  produce  a  column  of  incandescent  gas  of 
uniform  density  supplied  with  oxygen  at  every  point  within 
the  burning  mass.  This  condition,  it  was  supposed,  could 
only  be  fulfilled  by  employing  a  centrifugal  blower  forcing 
a  current  of  atmospheric  air  verticall}-  upAvards  through  a 
mass  of  easily-ignited  combustibles,  divided  into  small  pieces, 
placed  on  a  horizontal  grate.  Fig.  1  represents  a  conical  fur- 
nace, 2)rovided  with  a  grate  applied  at  the  contracted  lower 
portion,  admitting  of  a  free  passage  of  the  air  between  the 
Ijars  at  every  point.  A  capacious  chamber  is  formed  under 
the  grate.  Into  which  air  is  forced  by  an  ordinary  centrifugal 
blower.  The  internal  portion  of  the  furnace  is  contracted 
towai'ds  the  top,  as  shown  at  h  in  Fig.  2,  terminating  with 
a  square  opening,  over  which  is  placed  a  square  trunk  a, 
corresponding  exactly  with  the  said  opening.  The  furnace 
being  charged  with  combustibles  which  readily  ignite,  it 
will   be  evident   that  a  moderate  speed   of  the  blower  will, 


CHAP.  X.       tempeeatvue  of  the  solah  svbface.  201 

soon  after  ignitiou,  fill  the  square  trunk  with  a  dense  flamo 
of  perfectly  uniform  temperature  throughout,  contact  with 
the  exterior  atmosphere  being  wholly  prevented,  while  the 
air  which  supports  the  combustion  is  subdivided  almost 
inflnitely,  and  uniformly  disjDersed,  through  the  mass  of 
burning  fuel.  A  chimney,  the  section  of  which  is  equal  to 
that  of  the  contracted  part  of  the  furnace,  being  applied 
above  the  square  trunk,  any  tendency  to  pressure  and  accu- 
mulation in  the  same  will  be  effectually  prevented.  A  dense 
riame  of  uniform  temperature  having  thus  been  obtained,  its 
radiant  power  has  been  ascertained  by  the  folio-wing  device : 
A  conical  vessel  h,  open  at  the  large  end,  surrounded  Avith  a 
water-jacket  of  cylindrical  form,  shown  in  Fig.  2,  is  secured 
to  the  square  trunk,  a  circular  opening  e,  shown  in  Fig.  3, 
being  ftu-med  in  the  side  of  the  latter,  corresponding  w^ith 
the  open  end  of  the  conical  vessel.  Referring  to  Fig.  2,  it 
will  be  seen  that  a  perforated  diaphragm  d  (composed  of 
polished  silver)  is  inti-oduced  near  the  small  end  of  the 
conical  vessel.  A  thermometer  is  applied  near  the  circular 
perforation  of  the  diaphragm,  the  bulb  being  placed  exactly 
in  the  centre  line  of  the  vessel.  An  opening  /,  siuTOunded 
by  a  short  conical  tube,  covered  wnth  a  piece  of  mica,  affords 
a  view  of  the  interior  of  the  conical  vessel.  The  water- 
jacket  was  supplied  from  the  street-main,  a  constant  stream 
being  kept  up  during  experiments.  The  application  of  a 
chimney  of  large  diameter  above  the  square  flame-trunk, 
and  the  covei-ing  of  the  short  conical  tube  with  mica,  as 
stated,   in   order  to   prevent   currents   of  heated   air   or  gas 


202  EADIANT  HEAT.  CHAP.  x. 

from  circulating  tlirougla  tlae  conical  vessel,  have  contribi:ted 
to  secure  the  desired  result — viz.,  a  disc  of  flame  of  uniform 

r 

brightness,  the  color  varying  with  the  speed  of  the  blower.  i 

It  might  be  supposed  that  the  high  temperature  of  the  flame  ij 

would  at  once  destroy  the  square  trunlc.     Such,  ho^\"ever,  is  '^ 

not  the  case,  the  trunk  being  made  of  plate-iron  only  iV  in.  ,j 

thick,  the  radiation  of  which  is  so  rapid  that  the  gases  com- 
posing the  flame  cannot  communicate  the  heat  as  fast  as  it 
is  carried  ofE  by  external  radiation.  The  top  of  the  furnace 
at  the  point  where  the  flame  is  concentrated  and  conducted 
into  the  sqi;are  trunk,  being  exposed  to  intense  heat,  is  lined 
with  fire-clay.  It  should  be  borne  in  mind  that  the  apparatus 
is  exposed  to  a  high  temperature  only  while  the  blower  is 
in  operation,  the  motion  being  stoj^ped  as  soon  as  the  internal 
thermometer  reaches  maximum  indication. 

It  will  be  noticed  by  those  Avho  have  paid  attention  to 
the  demonstration  in  Chap  I.  that,  unless  the  radiant  surface 
forms  a  sj)herical  concavity,  the  focus  of  which  coincides 
Avith  the  centre  of  the  bulb  of  the  recording  thermometer, 
the  indication  Avill  not  be  exact.  The  flame-disc  being  ci/-- 
cular,  this  objection  may  be  overcome  by  removing  the  ther- 
mometer from  the  flame  to  such  a  distance  that  the  mean 
length  of  the  heat-rays  directed  to  the  bulb  corresj)onds 
with  the  radius  of  a  concave  radiator  of  the  same  diameter 
as  the  flame-disc.  For  the  sake  of  ready  comparison,  the 
diameter  of  this  disc  and  the  focal  distance  of  the  record- 
ing thermometer  have  the  same  relative  propoi'tions  as  in 
our  solar  pyrometer. 


CHAP.  X.  TEMPEBATUBE  OF  THE  SOLAR  SUEFACE.  203 

The  result  of  the  iuitiary  experiments  with  tlie  ajipuratiis 
thus  described  proved  that  the  temperature  transmitted  to 
the  focal  thermometer  by  the  radiation  of  the  flame-disc 
^vas  relatively  the  same  as  in  the  solar  pyrometer.  It  was 
inferred  from  this  fact  that  the  radiant  power  of  a  dense 
flame  with  active  combustion  kept  up  through  its  entire 
mass  is  the  same,  for  eqiial  temperatures,  as  the  radiant 
power  of  metallic  substances.  Further  investigation,  how- 
ever, disclosed  the  fact  that  this  unexpected  result  -was 
owing  to  the  circumstance  that  the  steam  emanating  from 
the  burning  fuel  during  the  experiment  had  entered  the 
conical  vessel,  and,  reaching  the  bulb  of  the  recording  ther- 
mometer, elevated  the  temperature  very  considerably.  The 
presence  of  steam  had  not  been  overlooked,  but  it  was  sup- 
posed that  the  rapid  circulation  of  cold  water  through  tlie 
jacket  surroimding  the  conical  chamber  would  produce  in- 
stant condensation.  It  is  much  to  be  regretted  that  before 
the  disturbing  influence  of  the  presence  of  steam  in  the 
chamber  containing  the  focal  thermometer  had  been  dis- 
covered, the  results  of  the  initiary  experiments  had  been 
published  in  several  mechanical  journals.  The  main  fea- 
ture of  the  apparatus  is,  however,  not  without  merit,  as 
probably  no  better  method  could  be  devised  for  produc- 
ing a  dense  flame  within  which  active  combustion  is  being 
kept  up  at  every  point.  In  combination  with  the  thermo- 
electric pile,  should  a  reliable  mode  of  calibration  hereafter 
be  devised,  there  is  reason  to  suppose  that  the  illusti-ated 
machine  may  prove  very  useful.     In  the  meantime,   I  have 


304  BADTANT  HEAT.  chap.  x. 

instituted  numerous  experiments  to  ascertain  tlie  radiant 
power  of  flames  as  compared  with  that  of  metallic  sub- 
stances. The  result  in  every  instance  proves  the  feebleness 
of  the  radiation  of  incandescent  gases  compared  with  incan- 
descent solid  substances  of  equal  temperature ;  but  until  the 
conclusion  of  tlie  investigation,  definite  statements  must  be 
deferred. 

Regarding  the  constitution  of  the  solar  surface,  the  tem- 
perature of  which  Ave  are  now  considering,  the  relative  feeble- 
ness of  its  emissive  power  compared  with  that  of  fused  iron, 
shown  by  our  investigations,  leads  irresistibly  to  the  conclu- 
sion that  we  are  dealing  with  an  incandescent  gas.  The 
constitution  of  the  solar  surface,  however,  has  nothing  to 
do  with  its  temperature.  But,  obviously,  our  endeavor  to 
ascertain  the  constitution  of  the  sun  will  prove  futile  until 
the  temperature  at  its  surface  be  first  established.  This  will 
be  readily  admitted.  Suppose  that  the  temperature  of  the 
sun's  surface  is  only  1,600°  C,  as  Pouillet  tells  us,  and  that 
the  solar  atmosphere  extends  to  the  moderate  height  of 
100,000  miles  above  the  photosphere.  It  may  be  shown,  by 
an  easy  calculation,  that  the  specific  gravity  of  the  gases  near 
the  solar  surface  Avould  under  these  conditions,  owing  to  the 
low  temperature,  the  depth  of  the  superincumbent  mass,  and 
the  great  attraction  of  the  sun's  mass,  exceed  tJiat  of  fused 
iron.  It  will  be  evident,  therefore,  that,  until  the  tempera- 
ture of  the  surface  shall  have  been  established,  investigations 
relating  to  the  constitution  of  the  interior  mass  and  the  sur- 
rounding atmosphere  cannot  lead  to  any  safe  conclusions. 


CHAP.  X.         TEMPEEATUEE  OF  THE  SOL.IE  SURFACE.  205 

I  now  propose  to  slaow,  by  a  demonstration  whioli  can- 
not be  objected  to,  that  the  high  temperature  established 
by  the  indications  of  the  sohxr  pyrometer  really  exists  on 
the  solar  surface.  Astronomers,  while  admitting  their  inabi- 
lity to  compute  the  degree  of  temperature  imjiarted  to  the 
surface  of  the  planets  of  our  solar  system,  OAving  to  the 
unknown  properties  of  their  atmospheres  in  retaining  the 
heat  received  from  the  sun,  have  no  hesitation  in  assigning 
the  exact  degree  of  solar  intensity  transmitted  to  the  atmo- 
spheric boundary  of  each  planet,  compared  with  that  ti'ans- 
mitted  to  the  boundary  of  our  atmosphere.  Sir  John  Herschel, 
in  treating  of  the  planet  Mercury,  does  not  admit  that  any 
donbt  exists  as  to  the  relative  degree  of  solar  intensity  to 
which  its  atmosphere  is  subjected.  The  mean  radius  of  the 
orbit  of  this  planet  being  to  that  of  the  earth  as  38  :  100, 
he  tells  us  that  the  temperature  produced  by  the  sun's  rays 
on  reaching  the  atmosphere  of  Mercury  is  nearly  seven 
times  greater  than  the  temperature  produced  by  solar  radi- 
ation at  the  boundary  of  the  terrestrial  atmosphere.  The 
following  extract  from  the  "Outlines  of  Astronomy"  sho^vs 
the  confidence  which  Sir  John  Herschel  places  in  the  appli- 
cation of  the  law  of'  inverse  squares  to  the  determination 
of  solar  energy  at  given  distances  :  "  The  intensity  of  solar 
radiation  is  nearly  seven  times  greater  on  ^fercury  than 
on  Earth,  and  on  Neptune  900  times  less ;  the  proportion 
of  the  two  extremes  being  that  of  upwards  of  5,600  :  1. 
Let  any  one  figure  to  himself  the  condition  of  our  globe 
were  the  sun  to  be  septupled,  to  say  nothing  of  tlie  greater 


20G  BABIANT  HEAT.  chap.  x. 

ratio  !  or  were  it  diminislied  to  a  seventli,  or  to  a  OOOth  ! 
It  is  true  that,  owing  to  the  remarkable  difference  between 
the  properties  of  radiant  heat  as  emitted  from  bodies  of 
very  exalted  temperature  as  the  sun,  and  as  from  such  as 
we  commonly  teim  tvai'in,  it  is  very  possible  that  a  dense 
atmosphere  surrounding  a  planet,  while  allowing  the  excess 
of  solar  heat  to  its  surface,  may  oppose  a  powerful  obstacle 
to  its  escape,  and  that  thus  the  feeble  sunshine  on  a  remote 
planet  .may    be    retained    and    accumulated    on    its    surface." 


No  doubt  Pouillet  would  have  felt  as  little  hesitation  as 
Herschel  in  determining  by  the  application  of  the  law  of 
inverse  squares  the  temperature  produced  by  solar  radiation 
on  Mercury.  Chapter  I.  contains  an  elaborate  demonstration, 
proving  the  correctness  of  this  law  with  reference  to  radiat- 
ing spheres  uniformly  heated  at  the  surface. 

The  above  diagram  represents  the  orbits  of  the  Earth, 
Venus,  and  Mercury,  their  relative  mean  distance  from  the 
sun  being  correctly  drawn.  The  orbit  of  an  imaginary  body 
I,  revolving  at  a  distance  of  10,000,000  miles  from  the  solar 


CHAP.  X.         TEMrEi:ATVliE-&F  THE  SOLAR  SURFACE.  207 

centre,  has  also  been  introduced  In  the  diagram,  for  the  pur- 
pose of  demonstrating  that  a  body  revolving  round  the  sun 
at  that  distance  would  be  exposed  to  a  temperature  gieatly 
exceeding  that  which  Pouillet  assigns  to  the  solar  suirface. 
Astronomers  agreeing  that  the  law  of  inverse  squares  holds 
for  all  distances,  whether  it  be  that  of  Neptune,  which  is 
30  times  further  from  the  sun  than  the  earth,  or  that  of 
Mercury,  whose  distance  from  the  luminary  is  less  than  -bV  of 
that  of  Neptune,  we  are  Avarranted  in  applying  that  law  to 
the  body  I,  shown  in  our  diagram,  supposed  to  revolve  at 
a  distance  of  ten  millions  of  miles  from  the  centre  of  the 
sun.  Let  us  then  calculate  what  degree  of  solar  intensity 
this  imaginary  body  will  be  subjected  to.  Our  calculations, 
obviously,  must  be  based  on  the  temperature  produced  by 
solar  radiation  at  the  boundary  of  the  earth's  atmosphere ; 
hence  it  will  be  necessary  fii-st  to  establish  that  temperature. 
Assuming  that  it  will  prove  more  satisfactory  to  persons 
having  obtained  their  knowledge  from  standard  physical 
works,  I  will  leave  out  of  sight  the  result  of  my  own  acti- 
nometiic  observations,  and  adojit  those  of  Pouillet,  the  dif- 
ference, besides,  being  quite  unimportant.  In  his  "  Elements 
de  Physique,"  published  at  Paris,  1856,  second  volume,  this 
savant  states,  with  reference  to  the  amount  of  heat  given 
out  by  the  sun :  "  In  the  vesical  passage  the  atmosphere 
absorbs  at  least  0.21  of  the  incidental  heat,  and  at  most 
0.27,  beyond  which  the  sky  ceases  to  be  serene ;  I  should 
add,  however,  that  the  28th  of  June,  on  which  day  the 
absorption   ■was    0.27,   a   light   white   veil   was  perceptible  in 


aOS  BABIANT  HEAT.  chap.  X. 

the  sky."  The  observed  and  commouly  accepted  maximum 
solar  intensity  on  the  ecliptic  being  68°  R,  it  will  be  found, 
by  adding  the  loss  of  heat  caused  by  atmospheric  absorp- 
tion— viz.,  0.21,  assumed  by  Pouillet — that  the  mean  tempe- 
rature produced  by  solar  radiation  at  the  boundary  of  the 
atmosphere  is  fully  86°  F.  The  mean  distance  of  the  earth 
being  in  round  numbers  92  millions  of  miles,  while  that  of 
the  imaginary  body  I  is  10  millions  of  miles,  from  the  sun, 
the  solar  intensity  to  which  the  latter  -would  be  exposed  is 
to  that  transmitted  to  the  boundary  of  the  terrestrial  atmo- 
sphere as  10'  :  92'  =  1  :  84.6.  Pouillet's  calculations,  and 
common  observations,  having,  as  before  stated,  established 
the  intensity  of  the  sun's  rays  on  entering  our  atmosphere 
to  be  nearly  86°  F.,  the  foregoing  analogy  proves  that  the 
supposed  body  I  will  be  subjected  to  a  radiant  intensity  of 
86°  X  84.6  =  7,275°  F.  We  have  thus  shown  by  a  method 
the  correctness  of  which  cannot  be  disproved  that  the  radiant 
heat  emanating  from  the  sun  (a  body  the  temperature  of 
Avhich,  Pouillet  informs  us,  is  under  3,000°  F.)  develops  an 
intensity  of  7,275°  Fahrenheit  at  a  distance  of  ten  millions  of 
miles.  Well-informed  persons  will  not  dispute  the  correctness 
of  the  foregoing  demonstration,  nor  ask  further  evidence  of 
the  erroneous  character  of  Secchi's  recent  speculations  or  the 
fallacy  of  Zollner's  and  Pouillet's  computations  assigning  a 
low  temperature  to  the  solar  surface. 


CHAPTER  XI. 

RADIATION  FllOM  INC.LNDESCENT  PLANES. 


Some  eminent  scientists  have  supposed  that  the  surface 
of  an  incandescent  body  projects  rays  of  equal  energy  in 
all  directions.  Laplace,  having  full  confidence  in  the  cor- 
rectness of  this  assumption,  founded  upon  it  the  demonstra- 
tion adverted  to  in  a  previous  chapter,  proving  that  the 
radiant  energy  which  emanates  from  the  receding  surface 
of  the  sun  possesses  greater  intensity  than  that  emanating 
fi-om  the  central  regions  of  the  luminary.  But  actual  obser- 
vation having  shown  that  the  radiant  energy  from  the  sun's 
border,  so  far  from  being  more  intense,  is  considerably  less 
than  fi-om  its  centre,  the  persistent  mathematician  was  driven 
to  the  alternative  of  proving  that  the  retardation  produced 
by  the  greater  depth  of  the  sun's  atmosphere  towards  the  limb 
neutralizes  the  assumed  increase  of  intensity  of  the  radiant 
heat.  How  satisfactorily  the  dexterous  analyst  proves  the 
startling  proposition  will  be  found  on  referring  to  "  M^ca- 
nique   Celeste,"   Tome   IV.   pp.    284-288 :    the   result   of   his 


a» 


210  BABIANT  HEAT.  chap.  xi. 

demonstration  leading  to  tlie  monstrous  assumption  that  the 
solar  atmosphere  absorbs  H  of  the  entire  energy  emanating 
from  the  radiant  surface.  Evidently  Laplace  did  not  regard 
solar  radiation  as  molecular  action  ca^iable  of  being  con- 
verted into  mechanical  energy,  or  he  would  have  perceived 
the  impossibility  of  H  being  absorbed  by  the  solar  atmo- 
sphere. It  is  not  intended  to  enter  on  a  criticism  of  the 
famous  demonstration,  but  the  question  is  so  intimately  con- 
nected with  the  subject  under  consideration  that  a  refei'ence 
to  the  main  points  is  called  for,  showing  on  what  grounds 
the  conclusion  was  based  that,  but  for  the  retardation  pro- 
duced by  the  solar  atmosphere,  the  I'adiant  energy  of  the 
luminary  would  be  increased  towards  the  border.  If  we 
admit  the  correctness  of  Laplace's  assumption  that  the  inten- 
sity of  radiation  increases  mth  the  obliquity  of  the  radiant 
surface  and  the  increased  number  of  rays  contained  in  a 
given  section,  we  must  also  admit  that  the  radiant  energy 
from  the  regions  near  the  sun's  border  will  be  greatly  en- 
hanced. And  since  it  has  been  found,  by  actual  observation, 
that  no  increase  of  intensity  takes  place,  the  inference  cannot 
be  resisted  that  the  retardation  produced  by  the  solar  atmo- 
sphere actually  neutralizes  the  increased  intensity  occasioned 
by  obliquity.  Accordingly,  the  retardation  may  be  deter- 
mined by  calculating  the  increase  of  intensity  corresponding 
with  the  obliquity  and  consequent  crowding  of  the  rays. 
But  this  calculation,  it  is  evident,  will  not  show  the  full 
extent  of  retardation,  since  not  only  is  there  no  inci'ease, 
but  a  considerable  diminyiion  of  intensity  towards  the  sun's 


CHAP.  XI.      KADIATIOX  Fi;O.M  IXVAXDESCBXT  PLAXES.  211 

border.  Hence,  the  amount  of  retardation  determined  agree- 
ably to  the  doctrine  tliat  the  radiant  intensity  is  increased 
by  the  obliquity  of  the  rays  will  be  still  further  augmented. 
The  reader  will  perceive,  from  this  exi^osition,  on  Avhat  erro- 
neous grounds  Laplace's  enunciation  is  based,  that  "if  the 
sun  were  stripped  of  its  atmosphere,  it  would  appear  twelve 
times  as  luminous." 

Tlie  foregoing  reference  to  doctrines  promulgated  nearly 
a  century  ago,  when  solar  radiation  was  but  imperfectly 
undei*stood,  will  be  deemed  inappropriate  by  those  who  do 
not  bear  in  mind  that  the  highest  authorities  of  the  present 
time  advocate  similar  doctrines.  Referring  to  Chapter  VI., 
it  will  be  seen  that  Pfere  Secchi,  who  has  devoted  more 
time  to  the  investigation  of  the  subject  than  any  one  else, 
presents  calculations  intended  to  prove  that  the  retardation 
offered  by  the  solar  atmosphere  to  the  passage  of  the  rays 
is  so  great  that  only  a  fraction  of  the  radiant  heat  enters 
space.  He  sums  xip  his  investigation  by  the  following  posi- 
tive statement :  "  1st.  At  the  centre  of  the  disc,  perpendicu- 
larly to  the  surface  of  the  photosphere,  the  absorption  arrests 
about  I,  more  exactly  ^,  of  the  total  energy.  2d.  The  total 
action  of  the  absorbing  envelope  of  the  visible  hemisphere 
of  the  sun  is  so  great  that  it  allows  only  t^V  of  the  entire 
radiation  to  pass,  the  remainder — that  is  to  say,  -i-A — being 
absorbed."  Pei-sons  accustomed  to  compare  mechanical  equi- 
valents, especially  those  who  possess  practical  knowledge  of 
the  amount  of  mechanical  power  developed  by  the  radiant 
heat  emitted  by  incandescent  bodies  at  definite  temperatures. 


312  RADIANT  HEAT  chap.  xr. 

positively  reject  all  assumptions  involving  any  considerable 
loss  of  radiant  energy  by  absorption  in  a  medium  perpetu- 
ally exposed  to  the  radiator.  Nor  will  the  assertion  that 
the  radiant  heat  is  converted  into  molecular  motion  within 
the  solar  envelope  be  accepted  by  any  j)ersou  comprehend- 
ing that  the  mechanical  energy  capable  of  being  developed 
by  the  heat-rays  projected  from  the  photosphere  must  enter 
space  less  only  the  amount  of  actual  toovTe  performed  during 
the  passage  through  that  envelope.  The  investigations  con- 
ducted by  means  of  the  solar  calorimeter  described  in  Chap. 
V.  have  shown  that  the  dynamic  energy  develo^jed  by  the 
sun's  radiant  heat  on  entering  the  earth's  atmosphere  amounts 
to  7.11  thermal  units  per  minute  upon  an  area  of  one  square 
foot,  while  the  dispersion  of  the  rays  is  in  the  ratio  of  1  :  45,400  ; 
hence,  each  square  foot  of  the  photosphere  emits,  as  shown 
in  the  chapter  referred  to,  322,000  thermal  units  per  minute. 
Secchi  says  that  only  i  of  the  heat  emitted  passes  through 
the  sun's  atmosj)here.  Accordingly,  7  X  322,000  =  2,254,000 
thermal  units  per  minute  are  absorbed.     Noav,  the  develop- 

33,000 
ment    oi   one   horse-power   requires  =  42.7    units   per 

minute ;  hence  the  energy  supjiosed  to  be  absorbed  repre- 
sents  a   mechanical   force,  continually  acting,   amounting   to 

2,254,000 

— -— - —  =  52,700  horse-power  for  each  square  foot  of  the 

surface  of  the  photosphere.  Considering  that  the  sun  is  sur- 
rounded by  highly  attenuated  gases,  containing  a  very  small 
quantity  of  matter,  Secchi's  assumption  that  the  stated  enor- 


CHAP.  XI.      UABIATTOy  FTtOM  INCANDESCENT  PLANES.  213 

luous  amount  of  energy  is  absorbed  by  tlie  sun's  atmosphere 
is  utterly  at  variance  Anth  tlie  laws  of  mechanics.  The  fore- 
.  going  discussion  has  been  deemed  appropriate  in  this  place, 
in  order  to  t-all  attention  to  the  importance  of  ascertaining 
the  true  energy  of  heat-rays  projected  from  incandescent  sur- 
faces at  acute  angles.  If  we  can  prove  by  positive  practical 
means  that  the  assumption  is  false  which  asserts  that  radia- 
tors emit  rays  of  equal  energy  in  all  directions,  we  destroy 
the  foundation  on  which  the  theory  rests  which  has  led  to 
the  conclusion  that  only  i  of  the  energy  developed  by  the 
sun  jienetrates  its  atmosphere. 

The  illustration  on  Plate  21,  referred  to  in  Chapter  VI., 
repi-osents  a  vertical  section  and  top  view  of  an  inverted 
conical  vessel,  the  bottom  of  which  is  concave,  the  top 
being  open  and  pi'ovided  with  a  wide  flange.  A  revolv- 
ing semi-sphi'rical  disc  of  cast  iron,  flat  on  the  under  side, 
is  suspended  on  two  transverse  axles  above  the  open  end  of 
the  conical  vessel,  the  axles  turning  in  appropriate  bearings 
resting  on  the  top  of  the  wide  flange  before  mentioned.  A 
lever  handle  is  secured  to  one  of  the  transverse  axles,  for 
the  purjiose  of  placing  the  disc  at  any  desired  angle,  the 
degree  of  inclination  l)eing  indicated  by  a  graduated  quad- 
rant applied  as  shown  in  the  illustration.  The  conical  vessel 
is  surrounded  by  a  jacket,  a  stream  of  water  being  circulated 
through  the  intervening  space  during  experiments.  The  incan- 
descent revolving  disc  is  protected  against  loss  of  heat  on 
the  top  bv  a  non-conducting  covering  composed  of  fire-clay, 
so  arranged  that  it  may  be  quickly  applied  and  removed.     A 


214  BABIANT  BEAT.  chap.  xt. 

semi-spherical  water-jacket  is  a})plie(I  aljove  the  revolving  disc, 
to  protect  the  same  from  the  disturbing  influence  of  currents 
■  of  air.  It  will  be  found,  on  examining  the  illustration,  that 
the  water-jacket  referred  to  is  placed  on  the  top  flange  of 
the  conical  vessel,  without  fastening;  hence  it  may  be  taken 
away  and  replaced  in  a  few  seconds.  The  jacket  surround- 
ing the  conical  vessel  being  maintained  at  a  constant  tempe- 
rature by  a  current  of  ^vater,  the  air  in  the  lower  part  will 
also  be  maintained  at  a  constant  temperature.  Obviously,  the 
heated  air  at  the  top  cannot  descend  to  the  bottom ;  conse- 
quently, the  bulb  of  the  recording  thermometer  will  be  influ- 
enced only  by  the  radiation  of  the  surrounding  vessel,  and 
by  the  radiant  heat  which  the  incandescent  disc  transmits. 
It  is  hardly  necessary  to  mention  that  the  lower  half  of  the 
bulb  is  protected  by  a  non-condiicting  covering.  In  view  of 
the  foregoing  explanation,  it  will  be  evident  that  the  mea- 
surement of  the  intensity  of  the  radiant  heat  projected  from 
the  incandescent  disc  towards  the  bulb  of  the  thermometer, 
at  different  angles  of  inclination,  will  be  as  reliable  as  if  the 
air  were  exhausted  from  the  conical  vessel.  In  either  case, 
the  temperature  of  the  surrounding  vessel  which  radiates 
towards  the  thermometer,  being  deducted  from  the  tempe- 
rature indicated  by  the  same,  shows  the  intensity  of  the 
radiant  heat  transmitted  to  the  bulb.  It  may  be  contended 
that  the  upper  part  of  the  latter  loses  a  small  amount  of 
heat  by  convection  attending  the  presence  of  air  ^vithin  the 
vessel.  Assuming  that  the  loss  of  heat  from  that  cause  is 
appreciable,  this  loss  will  be  proportionate  to  the   intensity 


CHAP.  XI.      BADIATION  FROM  nCAXDESCEST  PLANES.  215 

of  tlie  lieat  traiisiiiittecl  during  eacli  experiment ;  hence  it 
cannot  affect  the  relative  difference  of  intensity  for  different 
degrees  of  inclination  of  the  incandescent  disc. 

Dui'iug  experiments,  the  apparatus  is  placed  near  an  air- 
furnace,  hose  being  attached  to  the  nozzles  of  the  external 
casing  for  circulating  a  constant  stream  of  water  through  the 
intervening  space.  The  furnace  having  been  charged  with 
combustibles  capable  of  producing  a  steady  fire,  and  heated 
to  the  requisite  degree,  the  disc  is  inserted.  Having  remained 
in  the  furnace  until  the  color  of  the  metal  approaches  bright 
orange,  the  disc  is  quickly  withdrawn  and  placed  over  the 
open  conical  vessel,  supported  by  the  axles  shown  in  the  top 
view  of  the  illustration. 

Agreeably  to  the  theory,  the  correctness  of  which  we  are 
going  to  disprove,  the  incandescent  disc,  placed  at  the  incli- 
nation shown  in  the  illustration,  \\\\\  transmit  a  higher  tem- 
perature to  the  thermometer  than  if  it  were  placed  at  a 
greater  angle  to  the  vertical  line ;  the  reasons  assigned  for 
this  assumption  being  that  the  same  number  of  radiating 
points  are  presented  by  the  disc,  and  the  same  number  of 
rays  of  equal  energy  emitted  in  either  position,  while  in  the 
former  they  are  more  concentrated  than  in  the  latter.  The 
stated  assumption  involves  the  proi^osition  tliat  parallel  I'ays 
projected  at  an  acute  angle,  fi'om  a  given  number  of  radiating 
points,  transmit  greater  intensity  than  an  equal  number  t»f 
parallel  rays  projected  at  a  less  acute  angle  to  the  radiant 
surface.  That  this  proposition,  although  untenable,  is  very 
plausible,  will   be  seen  by  reference  to  Fig.    I    (see  diagram 


216  BADIANT  BEAT.  chap.  xi. 

Plate  22).  Let  a  b  represent  the  inclined  radiant  siu-face, 
and  a  c  h  the  several  radiating  points  projecting  heat-rays 
towards  the  sjjaces  d  f  and  Tc  g.  The  number  of  radiating 
points  and  the  number  of  heat-rays  projected  being  alike  in 
each  case,  while  the  space  represented  by  ^  ^  is  only  one- 
third  of  that  represented  by  d  f,  it  must  be  admitted,  if  we 
assume  all  rays  to  possess  equal  energy,  that  the  concentra- 
tion of  heat  within  h  g  is,  three  times  greater  than  within 
d  f.  In  other  words,  that  a  given  area  within  h  g  receives 
three  times  more  heat  than  an  equal  area  within  d  f.  This 
apparently  correct  view  of  the  question,  and  its  application 
to  spheres,  led  Laplace  astray  in  his  demonstration  concern- 
iug  solar  intensity.  In  the  next  chapter,  which,  as  already 
stated,  will  be  devoted  to  the  consideration  of  radiant  heat 
ti'ansmitted  from  incandescent  spheres,  the  influence  of  the 
spherical  form  on  radiant  intensity  will  be  fully  considered. 
Li  the  meantime,  we  must  admit  that  the  demonstration  con- 
tained in  Fig.  1  is  unanswerable  under  the  stijjulated  condition 
that  all  heat-rays  emitted  by  a  radiator  possess  equal  energy. 
Our  task,  therefore,  will  be  to  show,  lyractically,  that  the  stated 
condition  is  based  upon  false  assumptions,  tiaviug  already 
made  ourselves  acquainted  with  the  apparatus  constructed  for 
this  purpose,  we  may  at  once  proceed  to  consider  the  results 
of  the  experiments  which  have  been  instituted.  It  will  be 
evident  that,  owing  to  the  high  temperature  of  the  revolv- 
ing disc,  it  will  cool  very  rapidly  after  being  removed  from 
the  furnace  and  placed  in  position  over  the  conical  vessel, 
and  that  the  recording  thermometer,  however  sensitive,  will 


CiiAi'.  XI.      BAVIATION  FROM  INCANDESCENT  PLANES.  217 

require  so  long  a  time  before  reacliiug  maxiiuuiii  iiulication 
tliat  only  oiie  inclination  of  the  disc  can  be  experimented  on 
at  a  time,  thus  rendering  reheating  indispensable  for  each 
change  of  angle.  The  number  of  changes  of  inclination 
during  the  investigation  have,  therefore,  been  limited  to  ten, 
beginning  -with  90  deg.  and  ending  with  10  deg.  inclination 
to  the  vertic:il  line.  It  will  be  evident  that  the  high  tem- 
perature renders  it  practically  impossible  to  impart  exactly 
the  same  degree  of  incandescence  at  each  operation.  I  have, 
thei-efore,  resorted  to  the  expedient  of  maintaining  the  furnace 
at  a  uiiiforni  temperature,  and  to  expose  the  disc  to  the 
action  of  the  heat  duiing  an  equal  interval  of  time  for  each 
operation.  This  method,  though  not  precise,  has  conclusively 
established  the  fact  that  the  temperatiire  transmitted  to  the 
thei'uiometer  by  the  radiant  heat  varies  in  the  exact  ratio 
of  the  sines  of  the  mean  of  the  angles  formed  by  the  face 
of  the  disc  and  a  line  drawn  from  its  centre  through  the 
centre  of  the  bulb.  The  result  of  an  experiment  made  with 
great  care  will  be  found  recorded  by  the  diagram  Fig.  5,  in 
which  the  oi'dinates  of  the  curve  a  b  represent  the  sines  of 
the  angles  formed  by  the  disc  and  the  lines  mentioned,  the 
ordinates  of  the  irregular  line  c  d  e  representing  the  tempe- 
ratui'o  transmitted  to  tlie  recording  thernionietei'.  The  figures 
inserted  below  the  base  line  /'  g  show  the  number  of  degrees 
of  inclination  corresponding  with  the  sine  represented  by  each 
ordinate,  while  the  figures  above  the  curve  a  h  sho\v  the  dis- 
crepancy between  the  calculated  and  the  actn;d  temperature 
transmitted  to  the  thermometer.     It  will  be  found  ku  inspec- 


218  EABIANT  HEAT.  chap.  XI. 

tion  that  the  mean  diiference  of  the  actual  and  the  calcu- 
lated temperature  ahove  the  curve  is  1.94°,  that  below  the 
same  being  1.08° ;  hence  the  mean  discrepancy  is  only  0.86° 
Fah.  Considering  the  difficulty  of  imparting  an  equal  tem- 
perature at  each  operation  during  the  experiments,  this  dis- 
crepancy between  the  calculated  and  the  actual  temperature 
transmitted  by  the  radiation  of  the  incandescent  disc  is  unim- 
portant. We  are  warranted,  therefore,  in  adopting  the  con- 
clusion that  the  temperatures  vary  exactly  as  the  sines  of 
the  angles  of  inclination  of  the  radiant  surface.  It  has  been 
deemed  proper,  in  view  of  the  great  importance  of  this  con- 
clusion, and  in  order  to  render  the  subject  clearly  undei'stood, 
to  introduce  Figs.  4  and  5  combined,  showing  the  several 
angular  positions  of  the  incandescent  disc  during  the  inves- 
tigation. Dotted  lines,  it  Avill  be  seen,  have  been  introduced, 
connecting  these  angular  positions  with  the  corresponding 
ordinates  of  the  curve  a  h.  A  mere  glance  at  the  geome- 
trical representation  contained  in  Figs.  4  and  5  will  show 
that  the  temperatures  indicated  by  the  ordinates  of  the  curve 
a  h  correspond  exactly  with  the  sines  of  the  angles  of  incli- 
nation of  the  disc.  Bearing  in  mind  the  facts  thus  established, 
let  us  again  refer  to  Fig.  1,  in  which  the  space  h  g  \s  one- 
third  of  the  space  d  f.  We  are  now  enabled  to  demonstrate 
that  the  heat  transmitted  to  a  given  area  within  the  former 
is  only  one-third  of  the  heat  transmitted  to  an  equal  area 
within  the  latter.  Laplace  and  his  followers,  assuming  the 
reverse  to  be  the  case — viz.,  that  the  temperature  within  h  g 
will  be  three  times  higher  than  within  d  f — their  estimate  of 


CHAP.  XI.      RADIATION  FliOM  INCANDESCENT  PLANES.  219 

the  radiant  intensity  of  inclined  surfaces  will  obviously  be 
too  higb  in  tlie  inverse  ratio  of  the  sines  of  angles  of  incli- 
nation. The  consequence  of  this  grave  mistake,  with  reference 
to  the  radiant  power  of  incandescent  spherical  bodies,  will  be 
demonstrated  in  the  next  chapter,  containing  a  record  of  the 
temperatures  developed  by  the  heat-rays  projected  in  a  given 
direction  from  different  zones  of  a  metallic  sphere  raised  to 
a  hii^li  decree  of  incandescence. 


CHAPTER  XII. 


RADIATION  PROM  INCANDESCENT  SPHERES. 


The  question  wlietlier  equal  areas  at  different  points  of 
tlie  solar  surface  transmit  equal  energy  towards  the  earth 
has  engaged  the  attention  of  several  eminent  scientists.  It 
was  mentioned  in  the  previous  chapter,  on  radiation  from 
inclined  incandescent  planes,  that  the  author  of  "  Mecanique 
C61este,"  finding  by  observation  that  equal  areas  of  the  sun 
do  not  transmit  equal  energies  (the  central  portion  transmit- 
ting, in  opposition  to  his  reasoning,  much  greater  intensity 
than  those  near  the  border),  explains  the  matter  Ijy  sho^ving 
that  the  solar  atmosphere  retards  the  passage  of  the  rays, 
causing  a  great  diminution  of  the  energy  of  the  radiant  heat 
projected  from  the  border  of  the  sun  towards  the  earth.  It 
but  seldom  happens  thfit  questions  of  a  cosmical  nature  admit 
of  being  decided  by  actual  experiment,  the  present  being 
one  of  the  rare  instances  in  which  experimental  tests  may 
be  resorted  to.  Evidently,  if  the  great  retardation  of  energy 
towards  the  border,  demonstrated  by  Laplace,  is  caused  solely 
by  the  obstruction  encountered  during  the  passage  of  the  rays 

S30 


CHAP.  xii.      RADIATION  FBOil  INCANDESCE};!  SrUEliES.  221 

througL  tlie  atmosplieie  suriouiuling  the  sun,  the  receding 
surface  of  an  incandescent  spherical  body  not  sxirrounded  by 
a  retarding  mediuni  will  transmit  the  supposed  intensified 
radiant  heat  undiminished.  The  illusti'ation  on  Plate  28 
represents  an  apparatus  by  means  of  Avliich  it  has  been 
clearly  demonstrated  that,  notwitlistanding  the  absence  of 
a  retarding  mediuiu  round  an  incandescent  sphere,  the  sup- 
posed increase  of  radiant  energy  resulting  from  the  obli- 
quity of  the  heat-rays  projected  by  the  receding  surface 
does  not  take  place.  The  said  illustration  shows  a  vertical 
section  and  toj)  view  of  a  conical  vessel  sui'i'ounded  1)\  a 
water-jacket,  and  in  other  respects  consti'ucted  as  the  appa- 
ratus descril)ed  in  the  preceding  chapter.  The  top  flange 
of  the  conical  vessel  now  under  consideration  is,  however, 
provided  with  a  groove,  the  bottom  of  which  supports  a 
solid  sphere  of  cast  iron,  in  the  manner  shown  in  the  illus- 
tration. Belo^v  the  sj)here  are  inserted  two  semi-cylindrical 
screens  of  different  diameter,  each  composed  of  two  thin 
plates  of  iron,  the  intervening  space  between  these  plates 
being  filled  with  a  fire-proof  non-conducting  substance.  It 
will  be  seen,  on  carefully  inspecting  the  illustration,  that  the 
external  screen  is  annular  as  Avell  as  semi-spherical,  while  the 
central  screen  consists  of  a  concave  disc ;  hence  an  annular 
opening  is  formed  ])etween  each  pair  of  screens.  Supposing 
the  cast-iron  sphere  to  be  heated  before  being  placed  in  the 
position  represented,  it  will  be  evident  that  the  thermometer 
at  the  bottom  of  the  conical  vessel  will  only  receive  the 
radiant   heat  transmitted   Ijy  tlie  heat-rays  projected  towards 


232  BABIANT  HEAT.  chap.  xii. 

the  bulb  throngli  tlie  anmilar  opening  formed  bet^\'een  the 
two  screens.  It  will  be  readily  understood  that,  by  employ- 
ing screens  of  different  proportions,  zones  containing  equal 
convex  areas,  but  occupying  different  positions,  may  be  made 
to  radiate  towards  the  thermometer,  and  that  by  this  means 
the  radiant  intensity  transmitted  from  any  portion  of  the 
spherical  surface  may  be  ascertained.  Consequently,  we  are 
enabled  to  test  pi'actically  the  truth  of  the  assertion  that, 
but  for  the  intervention  of  the  sun's  atmosphere,  the  reced- 
ing solar  surface  would,  owing  to  the  increased  number  of 
rays  contained  within  a  given  section,  transmit  au  increased 
radiant  intensity  towards  the  earth.  It  may  be  urged  against 
our  device  that  atmospheric  air  intervenes  between  the  incan- 
descent sphere  and  the  recording  thermometer.  A  moment's 
consideration,  however,  will  show  that  the  consequent  retar- 
dation is  practically  inappreciable.  It  has  been  established 
in  preceding  chapters  that  the  retardation  sustained  by  the 
sun's  rays  in  passing  through  our  atmosphere  amounts  to 
0.207  on  the  ecliptic,  while  solar  intensity  at  the  boundary 
of  the  terrestrial  atmosphere  is  very  nearly  85°  F.  Conse- 
quently, the  loss  of  radiant  heat  hardly  reaches  18°  F.  in 
passing  through  28,800  feet  of  atmospheric  air  of  maximum 
density.  The  radiant  heat  of  our  experimental  a|)paratus 
being  transmitted  through  a  depth  of  only  2  feet,  tlie  retard- 
ing influence  of  the  air  intervening  between  the  ladiatiug 
sphere  and  the  bulb  of  the  recording  thermometer  \vill  be 

2  X  18° 
'^^^y  ~^^o~oa77  ~  0.0012°  F.    We  may,  therefore,  without  appre- 


CHAP.  XII.      EADIAl'lON  FEOM  IXCAXDESCENT  SPHERES.  223 

ciable  error,  assume  that  no  retarding  medium  surrounds  the 
experimental  incandescent  sphere.  The  princi2)al  features  of 
our  apparatus  having  thus  been  exphiiued,  and  the  nietliod  of 
solving  the  problem  under  consideration  pointed  out,  we  may 
now  proceed  to  consider  the  result  of  the  experiments  Avhich 
have  been  instituted.  In  order  to  facilitate  comparison,  the 
lower  half  of  the  sphere  visible  from  the  centre  of  the  bulb 
of  the  recording  thermometer  (see  Fig.  6  in  the  diagram  Plate 
24)  has  been  divided  into  four  zones,  A,  B,  C,  and  D,  contain- 
ing equal  areas.  It  w^ill  be  seen,  on  inspecting  the  arrangement 
of  screens  shown  in  the  diagram,  that  no  part  of  the  surface 
of  the  sphere  excepting  that  contained  within  the  parallel 
lines  defining  each  zone  is  capable  of  radiating  towards  the 
thermometer,  all  the  rest  being  shut  out  by  the  screens.  Ob- 
viously, the  latter  can  be  so  proportioned  that  the  radiant 
heat  from  any  part  of  the  lower  half  of  the  sphere  may  be 
projected  towards  the  bulb.  Figs.  3,  4,  5,  and  6  in  the  dia- 
gram show  the  arrangement  of  screens  adopted  in  our  expe- 
riments, by  means  of  which  the  transmitted  radiant  power 
of  each  of  the  zones  has  been  ascertained.  The  dimensions 
of  the  several  screens  have  been  determined  by  drawing 
radial  lines  from  the  centre  of  the  bulb  of  the  thermometer 
to  the  points  where  the  termination  of  the  zones  intei"sect 
the  circumference  of  the  sphere.  The  subject  will  be  most 
readily  understood  by  referring  to  Fig.  4,  which  exhibits 
zone  C.  The  screens  being  made  to  terminate  \vhere  they 
meet  the  radial  lines  p,  g  and  q,  g,  it  will  be  seen  that  an 
annular  opening  p  q  is  formed,   pennitting  all   heat-rays   to 


m  RADIANT  HEAT.  chap.  xil. 

pass  wLicli  are  projected  from  the  zone  C  in  tlie  direction 
of  the  Inilb  of  the  thermometer.  A  simihir  arrangement 
permits  the  radiant  heat  from  zone  B,  in  Fig.  5,  to  act  on 
tlie  thermometer,  lleferring  to  Fig.  3,  it  ^\•ill  be  found  that 
only  one  screen,  perforated  in  the  centre,  is  required  to  shut 
out  the  radiant  heat  from  the  thi'ee  upper  zones,  C,  B,  and 
A  ;  while  in  Fig.  6  the  radiation  from  the  three  lower  zones, 
D,  C,  and  B,  is  shiit  out  by  a  single  central  screen,  the  cir- 
cumference of  which  is  defined  by  the  radial  lines  m,  I:  It 
should  be  borne  in  mind  that,  although  the  several  screens 
are  represented  by  single  lines  in  the  diagram,  they  are,  as 
already  explained,  composed  of  double  plates,  a  fire-proof 
non-conducting  substance  being  inserted  between  the  two, 
the  object  of  which  is  self-evident. 

Referring  to  the  demonstration  contained  in  the  previous 
chapter  relating  to  the  diminution  of  energy  of  heat-rays 
projected  at  an  acute  angle  to  the  radiant  surface,  it  will  be 
seen,  on  mere  inspection,  that  the  upper  zones  represented  in 
<iur  diagram,  though  containing  an  equal  area  with  the  lower 
zones,  cannot  possibly  transmit  the  same  temperature  as  the 
latter.  The  advocates  of  the  views  expressed  in  "  Mecanique 
Celeste "  Avill  learn  with  surprise  that,  notwithstanding  the 
absence  of  an  intervening  retarding  medium,  so  great  is  the 
difference  of  energy  communicated  that,  while  the  zone  D, 
of  the  experimental  incandescent  sphere,  transmits  a  tempe- 
rature of  42°. 5  to  the  thermometer,  the  zone  A  transmits  only 
4°. 7.  The  latter  zone  being  further  from  the  thermometer 
than  the  foiiuer,  a  correction  is,  however,  necessary  on  account 


ciiAi".  XII.     EM'IATWN  FROM  IXCANDESCEST  SPUEIiES.  225 

of  the  iiicieaseJ  dLspersiun  of  tlie  Leat-rays  before  reaching 
the  bulb.  This  correction  being  made,  the  true  ratio  of  tem- 
perature transmitted  by  the  zones  D  and  A  \\  ill  be  42°.50  : 
6°.  19.  Consequently,  the  heat-rays  projected  fi'om  the  lower 
zone  of  the  incandescent  sphere  towards  the  bulb  of  the 
thermometer  transmit  nearly  seven  times  higher  temperature 
than  the  heat-rays  iwnn  the  upper  zone.  The  amount  of 
radiant  surface  being  alike  in  each  zone,  while  the  tempei'a- 
ture  of  the  sphere  is  uniform  throughout,  it  will  be  admitted 
that  owv  practical  test  has  clearly  demonstrated  the  feeble- 
ness of  the  he;it-rays  projected  from  the  border  of  an  incan- 
descent sphere  towards  a  given  point.  It  is  hardly  necessary 
to  add  that  each  zone  has  called  for  a  separate  experiment, 
rendering  reheating  of  the  sphere  indispensable  for  each. 
The  same  e.xpedieiit  has,  therefore,  been  resorted  to,  in  order 
to  insure  an  ecpial  degree  of  temperature  during  each  experi- 
ment, as  in  the  case  of  the  incandescent  inclined  disc  described 
in  the  previous  chapter.  Of  course,  it  has  been  found  iinprac- 
ticalde  to  impart  an  ecpial  temperature  to  the  sphere  at  each 
operation  ;  ])ut  this  difficulty  has  been  satisfactorily  overcome 
by  establishing  a  mean,  as  in  determining  the  intensity  of 
the  radiant  heat  transmitted  by  the  inclined  disc  refenvd 
to.  Besides,  the  result  has  been  checked  by  computing  the 
degree  of  temperature  capable  of  being  transmitted  to  the 
recording  therinometei'  by  each  zone,  in  accordance  with  the 
relation  wliicli  the  intensities  l^ear  to  the  angles  formed  by 
the  radiating  surface  and  the  heat-rays  projected  towards  the 
centre  of  the  bulb.     Before  giving  an  account  of  our  exjie- 


226  EABIANT  HEAT.  chap.  xii. 

riments,  let  us  demonstrate  theoretically  what  temperature 
each  zone  ought  to  communicate  to  the  thermometer,  in  con- 
formity with  the  fact  established  by  the  experiment  recorded 
in  the  preceding  chapter,  that  the  intensity  of  the  radiant 
heat  transmitted  by  an  incandescent  disc  is  directly  propor- 
tional to  the  sines  of  the  angles  formed  by  the  projected 
heat-rays  and  the  radiating  surface.  In  order  to  simplif}^ 
the  demonstration,  the  several  zones  have  been  divided  into 
halves  by  dotted  lines  (see  Fig.  7);  radial  lines  being  drawn 
to  the  thermometer  at  z  from  the  points  of  intersection  of  the 
dotted  lines  referred  to  and  the  circumference  of  the  sphere. 
Tangential  lines,  (/  f,  c  ii,  h  x,  and  a  y,  have  also  been  drawn 
from  the  said  points  of  intersection.  It  will  be  evident,  on 
considering  the  properties  of  spherical  zones,  that  the  radial 
lines  d  z,  c  z,  b  z,  and  a  z  represent  the  mean  direction  of 
the  heat-rays  projected  by  each  zone  respectively  towards  z. 
Hence  the  sines  of  the  angles  t  d  z,  to  c  z,  x  b  z,  and  y  a  z 
will  determine  the  amount  of  radiant  heat  transmitted  towards 
z  by  each  of  the  zones  D,  C,  B,  and  A.  Calculation  shows 
that  if  the  sine  of  the  angle  t  d  z  he  represented  by  unity, 
the  sines  of  the  other  angles,  in  the  order  presented,  will  be 
0.671,  0.384,  and  0.121,  while  the  experiments  which  have 
been  made  show  tliat  the  zone  D  transmits  a  temperature 
of  42°.50  to  the  recording  thermometer.  Consequently,  the 
zones  C,  B,  and  A  ought  to  transmit  respectively  28  .50, 
16°.31,  and  5°, 16  to  the  thermometer  at  z.  The  accompany- 
ing table  shows  to  what  extent  the  actual  temperatures 
transmitted  by  the  incandescent  sphere  differ  from  the  stated 


CHAP.  XII.      EADIATIOX  FROM  INCANDESCEUT  SPHERES. 


227 


computed  temperatures.  It  should  be  observed  tliat  no  di- 
rect comparison  can  be  based  upon  tlie  temperatures  entered 
in  the  fourth  column,  since  the  heat-rays  projected  by  the 
several  zones  are  subjected  to  different  degrees  of  dispersion, 
owing  to  the  unequal  distance  from  the  thermometer.  Due 
allowance  being  made  for  the  dispersion  of  the  rays,  in  con- 
formity with  the  elements  fiu-nished  in  Fig.  7,  the  consequent 
augmentation  of  temperature  has  been  added,  and  the  cor- 
rected values  entered  in  the  fifth  column  of  the  table.     The 


1 

2 

■s 

4 

5 

6 

§ 

Mean  angle  of 
projection. 

Comparative 
sine. 

Obserrcd 
temperature. 

Corrected 
temperature. 

Computed 
temperature. 

Dei/,  ^'n. 

Proportion. 

•  Fah. 

'Fah. 

°Fah. 

D 
C 
B 
A 

58     0 

34  40 

19    0 

5  55 

1.000 
0.671 
0.384 
0.121 

42.5 
24.2 
10.1 

4.7 

42.50 

27.49 

12.82 

6.19 

42.50 

28.50 

16.31 

5.16 

computed  temperatures  will  be  found  in  the  sixth  column. 
It  will  be  imagined,  at  first  sight,  that  the  figures  entered  in 
the  table  indicate  a  serious  discrepancy  between  the  observed 
and  the  computed  temperature.  That  such  is  not  the  case 
\n\\  be  found  on  referring  to  Fig.  8,  in  which  the  ordinates 
of  the  regular  curve  a  h  represent  the  computed  temperatures, 
while  the  ordinates  of  the  irregular  curve  a  d  c  represent 
the  observed  temperatures.  Obviously,  the  computed  and 
the   observed   energies   transmitted   by   the   radiation  of   the 


238  BABIANT  HEAT.  chap.  xii. 

incandescent  sjiliere  are  tnily  represented  by  the  supei-ficies 
contained  between  the  base  /  g  and  the  curves  a  h  and  a  d  c 
respectively.  Calculation  shows  that  these  superficies  are  as 
1.000  to  0.945.  Considering  the  small  amount  of  this  dis- 
crepancy, in  connection  with  the  difliculty  of  bringing  the 
heated  sphere  to  an  equal  degree  of  incandescence  duiing 
each  experiment,  Ave  are  warranted  in  asserting  that  the  in- 
stituted test  has  proved  conclusive,  and  that  the  inaccuracy 
of  the  doctrine  promulgated  in  "  Mecanique  Celeste,"  regard- 
ing the  radiant  energy  transmitted  by  the  rays  projected  from 
the  receding  sm-face  of  an  incandescent  sphere,  has  been  fully 
demonstrated. 


CHAPTER   XIII. 


RADIATION  FROM  FUSED   IRON. 


The  illustration  on  Piute  25  represents  a  calorimeter 
originally  constructed  to  demonstrate  practically  the  fallacy 
of  the  statements  contained  in  certain  papers  read  before 
the  Academy  of  Sciences  at  Paris  by  Messrs.  Saiute-Claire- 
Deville  and  M.  E.  Vicaire.  These  physicists  assert  that  the 
temperature  of  the  solar  surface  does  not  exceed  that  pro- 
duced by  the  combustion  of  organic  substances.  Their  rea- 
soning being  based  on  the  law  of  radiant  heat  established 
by  Dulong  and  Petit,  I  instituted,  soon  after  the  publication 
of  the  papers  referred  to,  a  series  of  experiments  on  a  very 
large  scale,  in  order  to  test  thoroughly  the  correctness  of 
that  law  AN-ith  reference  to  radiation  at  high  temperatures. 
The  nature  of  these  experiments  will  be  seen  by  the  fol- 
lowing brief  description :  An  iron  vessel,  lined  with  fii'e- 
clay  on  the  inside,  was  filled  with  fused  cast-iron  obtained 
from  a  cupola  furnace  in  wliicli  the  metal  had  been  raised 
to  a  temperature  exceeding  .'5,000'  F.  by  the  process  of  over- 


230  RADIANT  HEAT.  chap.  xiii. 

heating.  On  tlie  surface  of  this  fused  mass,  the  weight  of 
which  exceeded  7,000  pounds,  the  calorimeter  represented 
in  the  illustration  was  floated  while  registering  the  dynamic 
energy  developed  by  the  radiant  heat  of  the  metal.  Sir 
Isaac  Newton,  -whose  sagacity  perceived  that  radiation  ^vith 
i-eference  to  mechanics  is  simply  transmission  of  energy, 
assumed  that  the  quantity  of  heat  lost  or  gained  by  a  body 
in  a  given  time  is  j)i'oportional  to  the  difference  between 
its  temperature  and  that  of  the  surrounding  medium.  Some 
eminent  scientists,  however,  accepting  the  conclusions  and  for- 
mula of  Dulong  and  Petit  (see  Chap.  II.),  assert  positively 
that  the  stated  assumption  is  incorrect.  The  important  fact 
appears  to  have  been  overlooked  that  the  investigations  insti- 
tuted by  those  experimentalists  have  in  reality  established 
only  the  degree  of  conductivity  of  the  radiators  employed, 
under  certain  conditions,  but  by  no  means  their  true  radiant 
energy  at  high  temperatures.  Sainte-Claire-Deville  and  M.  E. 
Vicaire,  therefore,  commit  a  serious  mistake  in  assuming  that 
the  quantity  of  heat  transmitted  by  the  radiation  of  incan- 
descent bodies,  at  very  high  temj^eratures,  has  been  determined 
by  theii'  celebrated  coimtrymen.  The  fact  may  properly  be 
adverted  to  in  this  place  that  the  relation  between  the  time 
of  cooling  and  the  quantity  of  heat  transmitted  by  I'adiation 
which  Dulong  and  Petit  established,  misled  Pouillet  regarding 
the  temperatui'e  of  the  solar  surface,  which  he  computed  at 
l,4Gr  C,  or  at  most  1,761°  C.  It  will  be  well  to  bear  in 
mind  that  Pouillet  had  himself  ascertained  with  considerable 
accuracy  the  temjaerature  produced  by  solar  radiation  on  the 


CRAP.  XIII.  EADIATIOS  FEOM  FUSED  IliON.  231 

surface  of  the  eartli,  aud  also  the  retardation  suffered  during 
tlie  passage  of  the  rays  through  the  terrestrial  atmosphere. 
He  was,  therefore,  able  to  demoustrate  that  the  dynamic 
energy  developed  by  solar  heat  amounts  to  nearly  300,000 
thermal  units  per  minute  for  each  square  foot  of  the  surface 
of  the  sun.  Considering  the  imperfect  means  employed  by 
Pouillet,  his  "  pyrheliometer,"  the  near  approach  to  exactness 
of  his  determination  of  solar  energy  is  remarkable. 

Temperature  being  a  true  index  of  molecular  and  mecha- 
nical energy,  conclusively  established  by  the  exact  relation 
bet\veen  the  degree  of  heat  and  the  expansive  force  of  per- 
manent gases  under  constant  volume,  it  is  surprising  that 
Pouillet  did  not  perceive  that  an  intensity  of  1,461°  C.  or 
1,761°  C.  could  not  possibly  develop  on  a  single  square  foot 
of  surface  the  enormous  energy  represented  by  300,000  ther- 
mal units  per  minute.  M.  Vicaire,  adopting,  like  Pouillet, 
Dulong's  formula,  states  in  the  paper  presented  to  the  French 
Academy  that  "  an  increase  of  600°  is  sufficient  to  increase 
the  radiation  a  hundredfold,"  and  that  Pouillet  has  verified 
Dulong's  law  to  more  than  1,000°.  "  Supposing,"  he  observes, 
"that  beyond  this  temperature  the  law  ceases  to  be  true,  it 
cannot  be  absolutely  remote  from  the  tnith  for  the  tempera- 
tures of  from  1,400°  to  1,500°,  \\hioh  we  deduce  by  adopting 
the  law."  Saiute-Claire-Deville  concludes  his  essay  on  solar 
temperature  thus :  "  In  accordance  with  my  fii-st  estimate,  I 
believe  that  this  temperature  will  not  be  found  far  removed 
from  2,500°  to  2,800°,  the  numbers  which  result  from  the 
experiments  of  M.  Bunsen  aud  those  published  long  ago  by 


232  BABIANT  HEAT.  chap.  xiii. 

M.  Debray  and  myself."  The  Frencli  scientists  tlien  agree 
that  the  temperature  of  the  surface  of  the  sun  does  not 
exceed  the  intensity  produced  by  the  combustion  of  organic 
substances,  tlieir  grounds  for  this  assumption  being,  as  we 
have  seen,  Dulong's  formula  relating  to  the  velocity  of  cool- 
ing at  high  temperatures.  But  Dulong  and  Petit,  apart  from 
the  imperfections  of  the  means  which  they  adopted,  did  not 
carry  tlieir  investigations  practically  beyond  the  temperature 
of  boiling  mercury.  It  will  be  seen,  on  reference  to  Chap. 
II.,  that  their  formula  relating  to  high  temperatures  is  mere 
theory,  the  unsoundness  of  which  the  investigation  now  under 
consideration  has  established  in  the  most  conclusive  manner 
by  the  insignificance  of  the  radiant  power  developed  by  a 
mass  of  fused  metal  presenting  an  area  of  900  superficial 
inches,  30  inches  deep,  raised  to  a  temperature  of  3,000°  F. 
Before  describing  the  instrument  employed  in  determining 
the  radiant  energy  developed  by  the  stated  unprecedentedly 
large  mass,  I  deem  it  impoi-tant  to  point  out  briefly  the  con- 
dition of  the  fluid  metal  during  the  experiments.  In  the  first 
place,  the  temperature  was  sufficiently  high  to  produce  an 
intense  white  light,  luminous  rays  of  great  brilliancy  being- 
emitted  by  the  radiant  surface  during  the  trial ;  (2)  the  bulk 
of  the  fused  mass  being  adequate,  the  intensity  of  radiation 
was  sustained  ^\•itllout  appreciable  diniinutic:)n  during  the  time 
required  for  observation.  The  temperature  being  higher  than 
that  which  the  French  investigators  assign  to  the  sui-face  of 
the  sun,  Avliile  the  bulk,  as  stated,  was  sufficient  to  maintain 
the    temperature    of   the   fused    mass,    it    may    reasonably  be 


CHA  r.  XIII.  EA  DIA  HON  FliO.U  FUSED  IRON.  833 

asked  why  an  area  of  one  square  foot  of  our  experimental 
lumiuous  radiator  should  not  emit  as  much  heat  in  a  given 
time  as  an  oqual  area  of  tlie  solar  suiface,  if  the  tempera- 
tui-e  of  the  latter  he  that  assumed  by  Pouillet  ?  It  is  hardly 
necessary  to  observe  that  an  increase  of  tlie  dimensions  of 
the  radiating  mass  of  metal  to  ,any  extent  whatever  could 
not  augment  the  intensity  or  add  to  the  dynamic  energy 
developed  by  a  given  area.  It  has  been  shown  in  previous  • 
chapters  that,  agreeably  to  Dulong's  erroneous  formula,  the 
emissive  power  of  a  metallic  radiator  raised  to  a  temperature 
of  3,000°  F.  considerably  exceeds  Pouillet's  estimate  of  solar 
emission. 

Let  us  now  briefly  examine  the  illustrated  calorimeter, 
constructed  for  asceiiaining  the  mechanical  energy  developed 
by  the  radiation  of  a  fused  mass  of  cast-ii'on  raised  to  the 
temperature  of  3,000°  F.  Fig.  1  represents  a  vertical  section, 
and  Fig.  2  a  perspective  view ;  a  is  a  cylindrical  boiler, 
having  a  flat  bottom,  composed  of  thin  sheet-iron  0.012  in. 
thick,  coated  witli  lamp-black.  The  vertical  part  of  this 
boiler  is  surrounded  by  a  concentric  casing  Z»,  the  interven- 
ing space  being  filled  with  a  fii'e-proof  non-conducting  sub- 
stance. A  horizontal  wheel  revolving  on  a  vertical  axle  f7, 
and  provided  with  si.\  radial  paddles  attached  to  a  perforated 
disc  c  c,  is  applied  within  the  boiler.  An  open  cylindrical 
trunk  g  is  secured  to  the  perforated  disc  which  supports 
the  paddles.  The  vertical  axle  passes  through  the  top  of 
the  lioiler,  a  conical  pinion  being  secured  to  its  upper  termi- 
nation.    By  means  of  a  cog-wheel  h,  attached  to  the  hoi-izontal 


234  BABIANT  HEAT.  OHAP.  xin. 

axle  Ic,  and  geared  into  the  conical  jsinion,  rotary  motion  is 
communicated  to  tlie  paddles.  The  centrifugal  action  of  tlie 
latter  will  obviously  cause  a  rapid  and  uniform  circulation  of 
tlie  water  contained  in  tlie  boiler — indispensable  to  prevent 
tlie  intense  radiant  lieat  of  the  fused  metal  from  burning 
the  bottom.  The  boiler  and  mechanism  thus  described  are 
secured  to  a  raft  I  I,  composed  of  fire-bricks  floating  on  the 
top  of  the  fluid  metal.  By  this  means  it  has  been  found 
practicable  to  keep  the  bottom  of  the  boiler  at  a  given  dis- 
tance, very  near  the  surface  of  the  fused  mass,  while,  by 
moving  the  raft  from  point  to  point  during  the  observation, 
irregular  heating,  resulting  from  the  reduction  of  tempera- 
ture of  the  surface  of  the  metal  under  the  bottom  of  the 
calorimeter,  has  been  prevented.  The  radiant  heat  emanat- 
ing from  such  a  large  body  of  fused  metal  being  too  intense 
to  admit  of  the  axle  k  being  turned  dii-ectly  by  hand,  an 
intervening  shaft  of  considerable  length,  provided  with  a 
crank-handle  at  the  outer  end,  has  been  employed  for  keep- 
ing up  the  rotation  of  the  paddle-wheel  during  the  trial.  It 
is  scarcely  necessary  to  mention  that  the  intervening  shaft 
should  be  coupled  to  the  gear-work  by  means  of  a  "uni- 
versal joint,"  to  admit  of  the  necessary  movement  of  the 
raft  from  point  to  point  on  the  surface  of  the  liquid  metal. 
The  experiment,  repeated  several  times,  has  been  conducted 
in  accordance  with  the  following  programme :  The  boiler 
being  charged  with  pure  water,  the  paddle-wheel  should  be 
turned  at  a  moderate  speed  while  observing  the  temperature 
of  the  fluid,  the  thermometer  employed  for  this  purpose  being 


CHAP.  xni.  RADIATION  FliOM  FUSED  IRON.  235 

introduced  through  an  opening  m  at  the  top  of  the  boiler. 
The  temperature  being  ascertained,  the  calorimeter  should 
be  placed  on  the  raft  as  quickly  as  possible,  and  the  time 
noted.  As  soon  as  vapor  is  observed  to  escape  through  the 
opening  at  m,  the  instninient  must  be  instantly  removed,  the 
time  again  noted,  and  the  temperature  of  the  ^vater  in  the 
boiler  ascertained.  It  will  be  well  to  keep  the  paddle-wheel 
in  motion  until  the  last  observation  has  been  concluded. 

The  temperature  of  the  fused  metal  having  been  as  high 
during  our  experiments  as  that  of  the  solar  surface,  accord- 
ing to  the  computation  of  Pouillet  and  his  followers/  while 
the  thin  substance  composing  the  bottom  of  the  calorimeter 
has  been  brought  almost  in  contact  with,  and  consequently 
received  the  whole  energy  transmitted  by,  the  radiant  sur- 
face, the  reader  will  be  anxious  to  learn  what  amount  of 
dynamic  energy  has  been  developed  by  the  radiation  of  the 
metal  in  a  given  time  on  a  certain  area.  The  desired  infor- 
mation is  contained  in  the  following  brief  statement :  Allow- 
ance being  made  for  heat  absorbed  by  the  materials  composing 
the  paddle-wheel,  etc.,  the  instituted  test  shows  that  the  tem- 
perature of  a  quantity  of  water  weighing  10  lbs.  avoirdupois 
has  been  elevated  121°  F.  in  164  seconds  (2.73  min.),  the  area 
exposed  to  the  radiant  heat  being  63  sq.  in.     Hence  a  dynamic 

10  X  121       IM       ,  ^_     ,  ,        .,  .      - 

enerev  X  =  1,013  tliennal   units  per  min.  has 

^^        2.73  63  '■ 

been  developed  by  the  radiation  from  1  sq.  ft.  of  the  surface 

of  the  fused  metal  maintained  at  3,000°   F.,  against  300,000 

units  developed  by  tlie  radiation  of  1  sq.  ft.  of  the  solar  sur- 


336  BABIANT  HEAT.  chap.  xiii. 

face,  the  temperature  of  Avliicli,  agreeal^ly  to  the  calculations 
of  the  Frencli  physicists,  is  less  than  that  of  our  experimental 
radiator.     Comment  is  iinnecessarj. 

Some  advocates  of  Dulong  and  Petit's  theory  explain  the 
enormous  discrepancy  which  our  investigation  of  the  radiant 
power  of  fused  metal  discloses,  by  showing  that  their  law 
I'elates  to  the  velocity  of  cooliug,  and  not  to  the  amount  of 
dynamic  energy  parted  Avith.  That  Pouillet  regards  the  law 
as  referring  to  dynamic  energy  is  evident,  or  he  would  not 
have  attempted  to  establish  by  computations  based  upon  it 
that  an  energy  represented  by  300,000  thermal  units  could 
be  developed  in  one  minute  upon  an  area  of  one  square  foot 
by  a  body  whose  temperature  is  under  1,700°  C.  Before 
concluding  our  discussion,  let  us  consider  how  Dulong  and 
Petit's  law  is  regarded  by  practical  engineers,  who  are  more 
interested  in  its  infallibility  than  students  of  natural  philo- 
sophy. Mr.  Box,  in  his  "  Practical  Treatise  on  Heat,"  pub- 
lished 1868,  says,  with  reference  to  Dulong  and  Petit's 
investigations,  in  which  he  evidently  places  full  confidence : 
"  Dulong  has  given  rules  which  agree  well  with  experi- 
ments up  to  a  difference  of  temperature  of  468°  F.  This 
rule  is  a  very  difficult  one  to  apply,  but  it  may  be  put  in 
such  a  form  as  to  give  a  ralio  by  which  calculation  by  the 
simple  rule  may  be  easily  corrected.     The  rule  thus  becomes  : 

124.72  X  1.0077*  X  (1.0077'  -  1)         ^       . 

— =   R",    in    which    t  =  the 

temperature  of  the  absorbent,  or  recipient  of  radiant  heat ; 
T  =  the  excess  of  temperature  of  the  radiating  body  in  degrees 


cn.\i'.  xiri. 


liADIATIOX  FBOM  FUSED  IJIOX. 


237 


Centigrade ;  and  E,"  =  the  i-jitio  <>f  loss  of  heat  under  the 
given  temperatures."  The  author  of  tlie  "  Practical  Treatise 
on  Heat"  then  proceeds  to  construct  a  table  of  temperature 
and  ratio  of  loss  by  cooling ;  but  before  presenting  the  same 


Ml!.  Box's  Taulh  ov  tuk  Katio  of  Loss  of  Hf.at  at  very  Higu 
Tempek.vtures,  by  the  Formula  of  Dllon'g. 

Temperatui-e  of  the  heated  body. 

li. 

S   S  l^ 

Temperature  of 

the  body 

above  that  of 

the  air. 

Ratio  of  heat  at  diffe- 
rent temperatures. 

RadiatioD. 

Contact  of 
air. 

'Fah. 

'Fah 

•FoA. 

Satio. 

BaUo. 

490 

60 

60 
60 
00 
60 
60 
60 
00 
60 
60 
60 

450 

540 

720 

840 

1080 

1260 

1440 

1620 

1800 

2160 

2520 

3.10 
4.19 

7.17 
12.68 
23.01 
42.70 
80.67 
154.5 
.  299.7 
1159.0 
4604.0 

1.980 
2.085 
2.230 
2.378 
2.450 
2.540 
2.620 
2.693 
2.760 
2.880 
2.985 

600 

780 

900  Red,  just  visible 

1140     "            "             

1320  Dull  red 

1600  Dull  cherry  red 

1680  Cherry  red 

1860  Clear  red 

2220  Clear  orange 

2580  White,  bright 

to  his  readers  he  prefi.xes  the  following  observation  :  "  This 
table  shows  that  with  a  radiant  body  at  a  clear  red-heat  of 
1,800°  the  loss  is  about  300  1  times  the  amount  due  by  the 
simple  formula,  and  at  a  l^right  white-heat  of  2,580  it  rises 


238  BADIANT  HEAT.  chap.  xiii. 

to  4,604  ! !  times  tliat  amount."  If  any  doubt  existed  on  the 
subject,  tlie  author's  emphatic  exchimations  furnish  unques- 
tionable evidence  that  he  is  not  aware  of  the  fact  that  he  is 
propagating  a  mischievous  doctrine,  and  that  he  regards  the 
stated  extraordinary  ratios  as  true  measures  of  the  amount 
of  dynamic  energy  parted  with  at  high  temperatures. 

The  fallacy  of  Dulong  and  Petit's  formula  relating  to  high 
temjjeratures  having  been  conclusively  demonstrated  in  Chap. 
II.,  I  have  deemed  it  unnecessary  to  examine  the  calculations 
based  on  that  formula  contained  in  the  papers  presented  by 
Messrs.  Sainte-Claire-Deville  and  M.  E.  Vicaire  to  the  Aca- 
demy of  Sciences  at  Paris,  referred  to  at  the  commencement 
of  this  chapter. 


CHAPTER  XIY. 


RADIANT  HEAT  MEASUKED  BY  THE  THERMO-ELECTRIC 
METHOD. 


Melloni  asserts,  in  "  La  Tberinoclirose,"  that  the  calorific 
energies  imparted  to  a  thermopile  are  as  the  arcs  through 
which  the  needle  of  the  galvanometer  sweeps,  until  the  deflec- 
tion exceeds  13  degrees.  This  assumption  being  at  variance 
with  the  principles  of  dynamics,  its  correctness  calls  for  a 
thorough  investigation  before  it  can  be  accepted.  Intending 
originally  to  employ  the  thermo-electric  method  for  ascer- 
taining the  difference  of  the  radiant  energy  transmitted  by 
the  sun's  rays  from  diiierent  portions  of  the  solar  disc,  I 
carefully  investigated  the  subject,  and  found,  by  experi- 
mental test,  that  Melloni's  law  is  not  correct.  Theoretical 
demonstration  pointed  to  the  fact  that,  for  deflections  not 
exceeding  15  deg.,  the  calorific  energy  impai-ted  to  the  pile 
by  radiant  heat  is  very  nearly  as  the  square  root  of  the 
versed  sine  of  the  angle  of  deflection  from  zero.  It  may 
be  briefly  stated  that,  having  previously   resorted  to  various 


240 


BADIANT  HEAT. 


expedients  for  testing  roughly  tlie  relicability  of  the  assump- 
tion that  the  energy  is  as  the  arc  up  to  thirteen  deg.  deflec- 
tion— the  result  of  the  test  in  each  instance  proving  decidedly 
unfavorable  to  Melloni's  doctrine — I  undertook  the  construc- 
tion of  a  special  ajjparatus  for  calibrating  the  galvanometer 
applied  to  my  thermopile.  By  means  of  this  apparatus  the 
energy  developed  for  different  deflections  of  the  needle  from 
zero  to  35  deg.  has  been  accurately  determined.  Before 
describing   the    new    device,   it   will    be    proper   to   examine 


Melloni's  method  of  calibrating  galvanometers,  described  in 
the  work  referred  to;  especiall}-  since  its  supposed  correct- 
ness has  induced  several  eminent  physicists  to  accept  the 
assumption  that  the  energies  are  as  the  arcs  swept  by  the 
needle  from  zero  to  13  deg.  deflection.  "  Two  vessels  V  V 
(see  Fig.  17)  are  half  filled  -with  quicksilver,  and  connected 
by  two  short  wires,  separately,  with  the  terminations  G  G 
of  the  galvanometer.  The  vessels  and  wires,  arranged  as 
shown,  will  not  change  the  action  of  the  instrument ;  the 
thermo-electric   current   between   the   pile   and   the   galvano- 


CHAP.  XIV.  TUEBMO-ELEVTinc  21EASUEEMENT.  241 

meter  being  freely  kept  up  as  before.  But  if  we  establish 
a  communication  between  the  two  vessels  by  means  of  the 
wire  F,  a  portion  of  the  current  will  pass  through  this  wire 
and  then  return  to  the  pile.  The  quantity  of  circulating  elec- 
tricity in  the  galvanometer  will  then  be  diminished,  while 
the  deflection  of  the  needle  will  be  reduced.  Suppose  that 
by  this  expedient  we  have  diminished  the  galvanometric 
deviation  to  one-fourth  or  one-fifth — viz.,  that  the  needle 
indicating  10  or  12  degrees,  by  the  power  of  a  constant 
source  of  heat  located  at  a  given  distance  from  the  pile, 
recedes  2  or  3  degrees  when  part  of  the  current  is  diverted 
by  the  outside  wire.  If  we  then  cause  the  source  of  heat 
to  act  at  various  distances,  and  observe  in  each  case  the 
inaxinuini  deflection  and  the  least  deflection,  we  obtain  the 
necessary  data  for  determining  the  ratio  between  the  deflec- 
tion of  the  needle  and  the  energy  causing  that  deflection. 
To  make  the  matter  better  understood,  and  to  give  at  the 
same  time  an  example  of  the  manner  of  operating,  let  us 
take  the  numbers  bearing  on  the  application  of  the  method 
to  one  of  the  thermo-multipliers.  Let  the  outside  circuit  be 
interrupted,  and  the  source  of  heat  located  at  an  adequate 
distance  fi'om  the  pile  to  deflect  the  needle  not  moi-e  than 
5  degrees.  The  wii'e  being  then  passed  from  V  to  V,  the 
needle  falls  to  1.5;  the  connection  between  the  vessels  being 
again  interrupted,  and  the  source  of  heat  placed  near  enough 
to  produce  the  following  deflections  in  succession  :  5°,  10°,  15°, 
20°,  25°,  30°,  35°,  40°,  45°.  Applying  the  same  wire  between 
V  and  V  after  each  deflection,  we  obtain  the  followiua:  ener- 


243  EADIAKT  MEAT.  chap.  xiv. 

gles:  1°.5,  3°,  4°.5,  6°.3,  8°.4,  11°.2,  15°.3,  22°.7,  29°.7.  Sup- 
posing the  energy  equal  to  unity  Avhicli  is  necessary  to  cause 
tlie  needle  to  describe  arcs  corresponding  with  each  of  the 
first  degrees  of  the  galvanometer,  we  then  have  the  number 
5  as  an  expression  of  the  energy  corresponding  to  the  initial 
observation.     The  other  energies  are   readily  ascertained   by 

5 

the  relations :   1.5  :  5  =  a?  =  —  a  =  3.333,  where  a  indicates 

lo 

the  deflection  when  the  outside  circuit  is  closed.  Obviously, 
any  diminished  current  is  to  the  total  current  to  which  it 
corresponds  as  any  other  diminished  current  to  its  corre- 
sponding total  current.  Hence,  5,  10,  15.2,  21,  28,  and  37.3 
are  the  energies  corresponding  to  the  deflections  5°,  10°,  15°, 
20°,  25°,  and  30°.  In  this  presentation  it  will  be  seen  that 
the  energies  are  nearly  proportional  to  the  arcs  up  to  about 
15  degrees ;  but  beyond  this  deflection  the  proportionability  is 
at  an  end,  the  discrepancy  augmenting  with  the  arcs."  The 
energies  at  intermediate  degrees,  it  is  stated,  are  readily  ascer- 
tained by  calculation  or  by  the  graphic  method,  the  latter 
being  assumed  to  be  sufficiently  precise  for  the  purpose.  The 
accompanying  table  exhibits  the  corresponding  deflections  and 
energies  determined  by  Melloni  in  accordance  with  the  fore- 
going demonstration : 

The  constructor  of  the  table  observes  that  no  notice  has 
been  taken  of  deflections  under  13  deg.,  since  the  energies 
within  that  deflection  are,  as  he  supposes,  correctly  repre- 
sented by  the  arcs  swept  by  the  needle.  It  is  hardly  neces- 
sary to  call  attention  to  the  unsatisfactory  nature  of  the  fore- 


ni.vi'.  XIV. 


TllKUMO-ELECTlilC  ME.  1 6' L  HEMES T. 


243 


going  iiit'tliod  of  leturinug  part  of  the  electi'ic  current  by  the 
-w'nv  F,  fur  the  purpose  of  ascertaining  the  calorific  energies 
imparted  to  the  pile  by  the  radiant  heat  emanating  I'roin 
the  radiator.  Unless  we  adopt  some  ]iositive  means  of  mea- 
suring the  intensity  of  the  heat  to  which  the  face  of  the 
pile  is  subjected   at  the   instant   of  observing  the  deflection 


Melloni's  Table,  showing  the  Relation  betweek 

Deflection 

AND  Energy. 

u 

Energy  ex- 
erted. 

Energy  ex- 
erted. 

Deflection  of 
needle. 

13.0 

13.0 

19.0 

19.8     1      25.0 

28.0 

14.0 

14.1 

20.0 

21.0     1      26.0 

29.7 

15.0 

15.2 

21.0 

22.3 

27.0 

31.5 

16.0 

16.3 

22.0 

23.5 

28.0 

33.4 

17.0 

17.4 

23.0 

24.9 

29.0 

35.3 

18.0 

18.G 

24.0 

26.4 

30.0 

37.3 

of  the  needle  of  the  galvanometer,  the  relation  of  deflection 
and  calorific  energy  cannot  be  accurately  determined.  Now, 
the  demon-stration  contained  in  C'liap.  I.  proves  that  the  inten- 
sity of  radiant  heat  transmitted  through  a  given  space  by  a 
circular  radiatoi'  of  known  diameter  and  temperature  may  be 
determined  with  positive  accuracy.  Accordingly,  the  method 
of  calibrating  galvancmietei-s,  which  I  am  going  to  lay  before 
the  reader,  is  based  on  the  stated  demonstration  i:)roving  that 
a  correct    knowledge   of  form,   distance,  and    temperature  of 


244  EADIANT  HEAT. 


CHAP.  XIV. 


the  radiator  enables  us  to  ascertain,  with  absolute  precision, 
the  degree  of  calorific  energy  imparted  to  the  thermo-electric 
pile  during  the  investigation.  The  following  brief  descrip- 
tion of  the  apparatus  represented  by  our  illustration  (see  PI. 
26)  will  suffice  to  give  a  clear  idea  of  the  same  :  t,  table 
having  a  longitudinal  parallel  groove,  6  ins.  wide,  2  ins.  deep, 
formed  on  the  top.  h,  sliding  wooden  block,  12  ins.  square, 
1^  ins.  thick,  provided  with  a  j)arallel  projection  below  cor- 
responding Avith  the  groove  in  the  table,  and  admitting  of 
the  block  sliding  freely  from  end  to  end.  A  vertical  plate 
s,  20  ins.  high,  12  ins.  wide,  is  secured  to  the  sliding  block. 
p  represents  a  thermo-electric  pile  placed  on  the  top  of  the 
table.  The  vertical  plate  s  is  perforated  in  the  centre,  for 
the  purpose  of  supporting  a  cylindrical  boiler  r,  -1  ins.  in 
diameter,  provided  with  an  open  trunk  on  the  tojj,  through 
which  a  thermometer  is  inserted.  The  end  of  this  boiler 
pointing  towards  the  pile  is  concave,  while  the  opposite  end 
is  flat ;  a  spirit-lamp  being  applied  ixnder  the  same,  sup- 
ported by  the  sliding  block  h.  A  scale,  divided  into  100 
parts  of  one  inch  each,  is  attached  to  the  side  of  the  table, 
the  zero  of  this  scale  coinciding  with  a  pei-pendicular  line 
draAvn  from  the  face  of  the  thermo-electric  pile  ^>.  The 
extreme  j)oiut  of  the  concavity  of  the  boiler  r  being  in  line 
Avith  the  front  side  of  the  plate  s,  while  the  zero  of  the 
scale,  as  stated,  is  in  line  with  the  face  of  the  pile,  it  -will 
be  seen  that  the  distance  through  which  the  radiant  heat 
acts  may  be  regulated  by  simply  moving  the  sliding  block 
to  any  desired  division  on  the  scale.     A  metallic  screen  s', 


CHAi\  XIV.  TUEUMO-ELECTRIC  MEASUREMENT.  245 

2(t  ins.  high,  12  ins.  wide,  platrd  with  polished  silver,  is 
attaclied  to  the  vei-tical  plate  s,  in  order  to  prevent  the 
radiant  heat  of  the  latter  from  acting  on  the  thermo-electric 
pile.  The  metallic  screen  is  provided  with  a  central  perfo- 
ration, 4  ins.  in  diameter,  the  centre  of  which  coincides 
with  the  prolongation  of  the  axis  of  the  cylindrical  boiler. 
Regarding  the  temperature  of  the  lattei-,  it  will  be  seen  that, 
by  applying  the  spirit-lamp,  as  already  stated,  the  water  may 
be  kept  constantly  at  the  boiling  point,  since  any  excess  of 
heat  above  that  point  will  be  carried  off  by  the  steam  allowed 
to  escape  through  the  open  trunk  which  contains  the  thex'- 
mometer.  Accordingly,  the  thermo-electric  pile  j)  will  at  all 
times  be  subjected  to  a  definite  radiant  intensity  depending 
on  its  distance  from  the  radiator  /■;  while  the  graduated 
scale  attached  to  the  side  of  the  table  t  enables  the  experi- 
menter to  regulate  that  distance  rapidly  and  accurately.  In 
accordance  with  the  law  governing  the  transmission  of  heat, 
before  referred  to,  the  temperature  imparted  to  the  thermo- 
electric pile  p  will  bear  the  same  relation  to  the  differential 
temperature  of  the  boiler  as  the  square  of  the  radius  of  the 
semi-spherical  end  of  the  latter  bears  to  the  square  of  the  dis- 
tance of  the  same  from  the  face  of  the  pile.  Consequently, 
when  the  boiler  is  jilaced  as  shown  in  the  illustration,  the 
temperature  transmitted  by  radiation  may  be  ascertained  by 
the  following  calculation :  Assuming  that  the  thermometer 
inserted  through  the  open  tinink  at  the  top  of  the  boiler 
indicates  212°  F.,  and  that  the  tepmeratui'e  of  the  surround- 
ing air  is  70    F.,  the  intensity  of  the  radiant  heat  emanating 


246  BABIAKT  HEAT.  chap.  xiv. 

from  tLe  boiler  will  be  212  -  70  =  142°  F.  Now,  as  the 
position  of  tLe  block  b  is  siicli  tliat  the  concavity  r  coincides 
A\itli  tlie  aOtli  division  on  the  scale,  tlie  distance  between  tlie 
face  of  tlie  pile  and  the  radiating  surface  will  be  50  inches, 
while  the  I'adius  of  the  concavity  is  2  inches.  The  tempe- 
rature imjjarted  by  the  radiation  emanating  from  the  boiler 

2'  X  142 
will,  therefore,  amount  to =  0°.227  F.     The  calorific 

'  '  50' 

energy  transmitted  by  the  I'adiator  at  all  other  distances  may 
of  course  be  determined  by  a  similar  process  of  computation. 
Having  theoretically  determined  the  intensity  of  the  radiant 
heat  for  each  division  on  the  scale,  the  existing  relation 
between  the  deflection  and  the  computed  energy  will  be 
ascertained  simply  by  observing  the  corresponding  position 
of  the  needle  of  the  galvanometer.  Our  task,  however,  is 
that  of  ascertaining  the  calorific  energy  corresponding  with 
arcs  not  of  varying  length  swept  by  the  needle  of  the  galva- 
nometei',  but  arcs  each  measuring  shs  of  a  circle  commencing 
at  the  galvauometric  zero.  Evidently,  arcs  and  energies  are 
not  directly  comparable ;  hence,  we  must  ascertain,  experimen- 
tally, what  calorific  energy  corresponds  with  the  first  degree, 
or  the  first  half  degree,  of  deflection  of  the  needle  from  zero. 
It  has  already  been  stated  that  the  radiant  energy  emanating 
from  the  concave  face  of  the  boiler  is  142°  F.  when  the  tem- 
perature of  the  surrounding  air  is  70°  F.  Hence,  agreeably 
to  the  foregoing  process  of  calculation,  the  temperature  im- 
parted to  the  pile  when  the  boiler  is  placed  at  the  extreme 
end  of  the  scale — ^■iz.,  100  inches  from  the  face  of  the  pile 


CHAP.  XIV.  THEUMO-ELECTEIC  MEASUEEMEXT.  247 

2'  X  142 

— will  be —  =  0°.057  F.     Now,  such   are  the  propor- 

100'  '  ^     '■ 

t'umii  of  tlic  illu.^trated  apparatus  that,  when  the  dilVereiitial 
teiii2)eratiii-e  nf  tlie  Ixiiler  is  142°  F.  and  the  eoneave  face 
of  the  boiler  coincides  Avith  the  100th  division  of  the  scale, 
the  detlection  of  the  needle  is  30'  from  zero.  The  forefjoins; 
demonstrations  and  reasoning  being  deemed  sufficiently  expla- 
natory, Ave  may  now  consider  the  diagram  attached  to  the 
illustration,  Plate  20.  The  length  of  the  ordinates  of  the 
curves  hf  and  !>  (/represent  the  relation  between  the  energies 
imparted  to  the  pile  and  the  arcs  swept  by  the  needle  ;  the 
figures  marked  on  the  vertical  base-line  a  c  denoting  the  degrees 
of  deflection  from  zero.  In  other  Avords,  the  ordinates  of  the 
curve  h  d  shoAv  the  observed  deflections  for  each  degree  from 
zero,  while  the  oi'dinat(>s  of  the  curve  h  f  show  the  developed 
energy.  It  Avill  be  seen,  therefore,  that  the  portions  of  the 
ordinates  Avhich  are  contained  between  the  two  ctii'ves  lepre- 
sent  the  excess  of  developed  energy  above  that  of  the  observed 
deflection.  Considering  that  the  length  of  the  ordinates  of 
the  curve  b  f  have  been  detenuined  in  accordance  with  the 
well-established  laws  governing  the  transmission  of  radiant 
heat,  while  the  length  of  the  ordinates  of  the  curve  h  d  is 
the  result  of  actual  observation,  the  correctness  of  the  ascer- 
tained rehition  cannot  be  qiiestioned.  Conserpiently,  a  mere 
inspection  of  the  diagram  suffices  to  show  the  fallacy  of 
Melloni's  assumption  that,  Avithin  a  deflection  of  13  degrees, 
the  arc  swept  by  the  needle  and  the  energy  imparted  to  the 
pile  correspond  exactly.     Obviously,  by  comparing  the  inter- 


348 


IIABIANT  HEAT. 


CHAP.   XIV. 


'1 

'able  a, 

snowiNfi 

THE   ReL 

\TION    BETWEEN 

Energy 

\ND 

Deflection  at  Depinite  Distances. 

2- 

.2          1 

II 
So 
O 

"o 

^1 

i 

a 

a 
o 

If 

II 
go 

Inches. 

'  Fah. 

Relative. 

Beg. 

IncTies. 

°  Fah. 

Relative. 

Deg. 

100 

0.057 

0.50 

0.50 

34 

0.491 

4.31 

3.80 

95 

0.063 

0.55 

0.60 

33 

0.521 

4.58 

4.00 

90 

0.070 

0.61 

0.70 

32 

0.555 

4.87 

4.30 

85 

0.078 

0.68 

0.80 

31 

0.591 

5.19 

4.50 

80 

O.OSS 

0.77 

0.90 

30 

0.631 

5.54 

4.90 

75 

0.101 

0.88 

1.00 

29 

0.675 

5.92 

5.30 

70 

0.116 

1.01 

1.10 

28 

0.724 

6.36 

5.60 

65 

0.134 

1.17 

1.20 

27 

0.779 

6.84 

6.00 

60 

0.158 

1.38 

1.40 

26 

0.840 

7.37 

6.40 

55 

0.188 

1.64 

1.60 

25 

0.909 

7.98 

6.90 

50 

0.227 

1.99 

1.80 

24 

0.986 

8.65 

7.30 

49 

0.236 

2.07 

1.90 

23 

1.073 

9.42 

8.00 

48 

0.246 

2.16 

2.00 

22 

1.173 

10.30 

8.90 

47 

0.257 

2.26 

2.10 

21 

1.288 

11.30 

9.90 

46 

0.268 

2.35 

2.20 

20 

1.420 

12.46 

10.90 

45 

0.280 

2.46 

2.30 

19 

1.573 

13.80 

12.00 

44 

0.293 

2.57 

2.40 

18 

1.753 

15.38 

13.10 

43 

0.307 

2.69 

2.50 

17 

1.965 

17.24 

14.40 

42 

0.322 

2.82 

2.60 

16 

2.219 

19.46 

16.30 

41 

0.338 

2.96 

2.70 

15 

2.525 

22.14 

18.50 

40 

0.355 

3.11 

2.90 

14 

2.898 

25.42 

20.40 

89 

0.373 

3.27 

3.00 

13 

3.361 

29.48 

23.00 

38 

0.393 

3.45 

3.00 

12 

3.944 

34.59 

25.90 

37 

0.415 

3.64 

3.10 

11 

4.694 

41.18 

29.00 

36 

0.439 

3.85 

3.30 

10 

5.680 

49.82 

32.00 

35 

0.464 

4.07 

3.50 

9 

7.012 

61.51 

35.00 

CHAP.  XIV.  THEEMO-ELECTEW  MEASUEEMENT.  249 

vening  space  between  the  curves  b  J  and  b  f  on  tlie  13th 
ordinate,  and  the  length  of  that  ordinate  between  the  base-line 
a  c  and  curve  b  d,  we  obtain  a  definite  idea  of  the  magnitude 
of  the  error  involved  in  Melloni's  doctrine  that  deflection  and 
enei'gy  correspond  until  the  position  of  the  needle  marks  thir- 
teen degrees  from  zero.  It  is  important  to  observe  that  a 
scale,  corresponding  with  the  scale  of  inches  marked  on  the 
side  of  the  table  represented  in  the  illustration,  has  been 
introduced  parallel  with  the  vertical  base-line  a  c  in  the 
diagram.  This  expedient  enables  us  to  make  a  direct  com- 
parison between  the  position  of  the  concave  radiator  and 
the  deflection  of  the  needle  of  the  galvanometer,  marked  on 
the  vertical  base-line  a  c.  It  wull  be  seen,  for  instance,  that, 
when  the  deflection  of  the  needle  is  35  degrees,  the  radiator 
is  placed  9  inches  from  the  face  of  the  pile. 

Let  us  now  consider  briefly  the  manner  of  conducting  the 
experiments  which  have  enabled  us  to  constioict  the  diagram 
referred  to  and  the  accompanying  table  A.  The  deflections 
of  the  needle  of  the  galvanometer  and  the  energies  imparted 
by  radiation  to  the  pile  beyond  the  50th  division  being  very 
small,  the  observations  between  that  division  and  the  termi- 
nation of  the  scale  have  been  confined  to  spaces  of  5  inches 
each,  as  will  be  seen  on  reference  to  the  table  mentioned. 
But  from  the  50th  to  the  9th  division  the  observations  have 
been  made  for  each  inch.  Accordingly,  41  distinct  experi- 
ments were  instituted  while  advancing  the  boiler  from  the 
fiftieth  to  the  ninth  division  of  the  scale  attached  to  the 
side  of  the  table.     It  is  important  to  mention  that,  in  order 


250  RADIANT  HEAT.  chap.  xiv. 

to  allow  tlie  pile  to  cool  effectually,  the  sliding  block  h, 
together  with  the  boiler  and  screens  s  and  s',  were  removed 
into  an  adjoining  room,  and  the  needle  of  the  galvanometer 
brought  to  perfect  rest  at  zero,  for  each  observation.  It  may 
be  mentioned  that  the  final  investigation  was  carried  out 
under  very  favorable  conditions,  the  temperature  of  the  sur- 
rounding air  fluctuating  so  slightly  that  the  differential  tem- 
perature of  the  boiler  did  not  vary  one  degree  during  the 
experiment.  The  mode  of  constructing  Table  A,  which  exhi- 
bits the  relation  between  energy  and  deflection  at  definite 
distances,  will  be  readily  understood.  The  distance  between 
the  concave  radiator  and  the  face  of  the  pile,  it  will  be 
seen,  has  been  entered  in  the  first  column,  while  the  tempe- 
rature transmitted  to  the  pile  by  radiation  has  been  entered 
in  the  second  column.  The  determination  of  the  temperature 
referred  to  is  effected  by  the  following  simple  arithmetical 
process :  Multiply  the  squai'e  of  the  I'adius  of  the  concave 
surface  r  by  the  differential  temperature  of  the  boiler,  and 
divide  the  product  by  the  square  of  the  distance  between 
the  radiator  and  the  pile  ;  the  quotient — entered  in  the  second 
column  of  the  table — expresses  the  intensity  transmitted  to  the 
pile  by  the  heat  emanating  from  the  radiator.  For  example, 
the  intensity  of  the  transmitted  radiant  heat,   at  a  distance 

2'  X  142 
of  19  inches,  -will  be  — —  =  1°.573  F.     Eef erring  to  the 

table,  it  Avill  be  found  that  the  temperature  thus  ascei'tained 
is  recorded  in  the  second  column,  opposite  the  distance  19 
entered  in  the  first  column.     The  mode   of  ascertaining  the 


CHAP.  XIV.  TnEBMO-ELECTRIV  MEASUREME^'T.  251 

temperature  transmitted  by  tlie  radiator  to  the  thermo-electric 
pile  at  each  poiut  of  the  scale  being  thus  fully  explained, 
let  us  now  consider  the  relative  amount  of  energy  repre- 
sented by  the  temperature  entered  in  the  second  column  of 
our  table.  It  has  already  been  pointed  out  that  the  tempe- 
rature imparted  to  the  pile  by  the  radiant  heat,  and  definite 
arcs — say  degrees — swept  by  the  needle  of  the  galvanometer, 
are  not  comparable  quantities ;  hence  cannot  be  determined 
by  calculation.  We  must  therefore,  as  already  pointed  out, 
have  recourse  to  the  experimental  process  in  ascertaining  the 
relation  of  the  temperature  transmitted  and  the  deflection  of 
the  needle  when  the  radiator  is  at  maximum  distance  from 
the  thermo-electric  pile.  Repeated  trials  have  shown  that, 
when  the  radiator  is  placed  at  a  distance  of  100  inches 
from  the  face  of  the  pile,  the  ratio  between  the  deflection 
of  the  needle — measured  by  arcs  containing  tJt  of  a  circle ; 
and  the  temperature  transmitted  to  the  pile — measured  by 
degrees  of  Fahrenheit,  is  as  0.50  to  0.57.  The  energies 
inserted  in  the  third  column  of  the  table  have  been  deter- 
mined in  accordance  with  the  stated  relation  of  temperature 
and  deflection  of  the  needle  of  the  galvanometer,  while  the 
deflections  of  the  needle  entered  in  the  fourth  column  have 
been  determined  by  observation.  It  will  be  seen,  by  inspect- 
ing the  latter,  that  the  energy  exceeds  that  indicated  by  the 
deflection  of  the  needle,  for  all  distances  between  the  55th 
division  on  the  scale  and  the  pile ;  the  energy  at  that  point 
being  1.64,  while  the  deflection  is  only  1.60.  Between  the 
100th   and   60th   divisions  of  the  scale  the  observed  deflec- 


252 


BABIANT  HEAT. 


CHAP.  XIV. 


tions,  it  mil  be  noticed,  are  irregular,  slightly  exceeding  tlie 
energies.  This  ii'regiilarity  is  occasioned  by  the  sensitiveness 
of  tlie  instrument  when  the  radiator  is  far  from  the  pile.  It 
only  remains  to  call  attention  to  Table  B,  exhibiting  the  final 
result  of   our  elaborate   investieation   of  the   thermo-electric 


Table  B,   showing  the  Eelation  between   Deflection 
AND  Energy. 

Deflection  of 
needle. 

Energy  ex- 
erted. 

Deflection  of 
needle. 

Energy  ex- 
erted. 

Deflection  of 
needle. 

Energy  ex- 
erted. 

Deg. 

Relative. 

Deg. 

Relative. 

Deg. 

Relative. 

1 

2 

3 

4 

6 

6 

7 

8 

9 

10 

11 

12 

0.89 

2.17 

3.38 

4.59 

5.77 

6.86 

8.00 

9.15 

10.33 

11.53 

12.75 

14.00 

13 

14 

15 
16 
17 
18 
19 
20 
21 
22 
23 
24 

15.28 
16.58 
17.90 
19.24 
20.60 
21.98 
23.39 
24.84 
26.34 
27.90 
29.53 
31.25 

25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 

33.07 
35.00 
37.05 
39.24 
41.58 
44.20 
47.00 
50.00 
53.30 
57.00 
61.23 

method  of  measuring  radiant  heat.  It  will  be  seen,  on  care- 
fully examining  this  table,  that  the  deflection  of  the  needle  of 
the  galvanometer  at  the  termination  of  the  first  degree  exceeds 
the  energy  transmitted  by  the  radiator  towards  the  thermo- 
electric pile  in  the   ratio    of    100   to   89,   difference  =  0.11  ; 


CHAP.  XIV.  THEBMO-ELECTBIC  MEASXTREMENT.  253 

an  uninipoii:aiit  irregularity  already  adverted  to.  Beyond  90' 
from  zero  tlie  energy  becomes  greater  than  the  deflection  in 
a  constantly  increasing  ratio  as  the  arcs  swept  by  the  needle 
augment.  Accordingly,  when  the  needle  has  moved  through 
an  arc  of  13  degrees,  the  energy  is  greater  than  the  deilec- 
tion  in  the  ratio  of  15.28  to  13.00,  instead  of  being  exactly 
balanced,  as  stated  by  Melloni. 


CHAPTER  XY. 


THE  THEEMOHELIOMETER. 


The  calculations  presented  by  Pere  Secchi  in  his  work 
"  Le  Soleil,"  relative  to  the  intensity  of  solar  radiation  and 
the  temperature  of  the  sun,  being  based  on  the  indications 
of  his  thermoheliometer,  I  have  carefiilly  examined  the  pro- 
perties of  this  unique  device,  delineated  on  page  267  of  the 
work  referred  to.  The  accompanying  illustration  (see  Fig.  1) 
represents  a  longitudinal  section  of  the  same  through  the  ver- 
tical plane.  A  B  and  C  D  are  two  concentric  cylinders  sol- 
dered one  to  the  other ;  they  form  a  kind  of  boiler,  the 
annular  space  being  filled  with  water  or  oil  at  any  tempe- 
rature. A  thermometer  t  passes  through  a  tube,  across  the 
annular  space,  to  the  axis  of  the  cylinder ;  it  receives  the 
solar  rays  introduced  through  a  diaphragm  m  •??,  the  opening 
0  of  which  is  very  little  larger  than  the  bulb  of  the  thermo- 
meter. A  thick  glass  v  closes  the  back  part  of  the  instrument, 
and  admits  of  ascertaining  whether  the  thermometer  is  placed 
in  a  direct  line  with  the  pencil  of  rays.     The  interior  cylinder 

254 


THE   TEEBMOEELIOMETEB. 


255 


and  the  thermometer  t  are  coated  with  hmip-Llack.  A  second 
thermometer  t'  shows  the  temperature  of  the  annular  space, 
and  consequently  that  of  the  enclosure.  The  A\hole  apparatus 
is  mounted  on  a  support  having  a  j)arallactic  movement,  to 
facilitate  following  the  diurnal  motion  of  the  sun.  The  appa- 
ratus being  exposed  to  the  sun,  it  will  be  found,  on  observing 
the  two  theimometers,  that  their  difference  of  temperature 
increases  gradually,  and  that  in  a  short  time  it  ends  by  being 
constant. 


Before  pointing  out  the  peeuliaiities  of  the  contrivance 
thus  described  by  Pcre  Secchi,  it  will  be  instructive  to 
examine  his  "  solar  intensity  apparatus,"  manufactured  by 
Casella,  represented  in  Fig.  2.  The  manufacturer  publishes 
the  following  statement  regarding  this  instmment ;  "  Two 
thermometers  are  here  kept  immersed  in  a  fluid  at  any 
temperature,  and  a  third  surrounded  by  the  same  conditions, 
but  not  immersed,  is  exposed  to  the  rays  of  the  sun.     The 


256  BABIANT  HEAT.  CHAr.  XT. 

increase  of  temperature  tlius  obtained  is  found  to  be  tLe 
same,  irrespective  of  the  temperature  of  tlie  fluid  ■wliicli  sur- 
rounds it."  No  one  acquainted  with  the  principles  which 
govern  the  transmission  of  heat  within  circuhiting  fluids  can 
fail  to  observe  that  the  thermometers  applied  above  the 
central  tube  will  not  furnish  a  reliable  indication  of  the 
temperature  of  the  fluid  below  the  same,  nor  of  any  portion 
of  the  contents  of  the  annular  space  towards  the  bottom. 
Apart  fi'om  this  defect,  it  will  be  j)erceived  that  an  upward 
current  of  atmospheric  air  will  sweep  the  under  side  of  the 
external  cylinder,  causing  a  reduction  of  temperature  of  the 
fluid  confined  in  the  lower  half  of  the  annular  sjjace.  Again, 
the  heat  radiated  by  the  bulb  of  the  thermometer  exposed 
to  the  sun  will  elevate  the  temperature  of  the  air  within 
the  central  tube,  and  consequently  produce  an  internal  circu- 
lation tending  to  heat  the  upper  part  of  the  fluid  contained 
in  the  annular  space.  The  effect  of  the  irregular  heating 
and  cooling  thus  adverted  to  will  be  considered  after  an 
examination  of  the  result  of  some  observations  recoi'ded  in 
Tal)les  A  and  B,  which  I  conducted  at  different  times 
during  the  month  of  September,  1871.  In  order  to  insure 
an  accurate  position,  the  instrument  during  these  observa- 
tions was  mounted  in  a  revolving  observatory  upon  a  table 
turning  on  declination  axes  provided  with  appropriate  mecha- 
nism and  declination  circle.  An  actinometer  being  attached 
to  the  same  table,  the  true  intensity  of  the  radiant  heat,  as 
well  as  the  sun's  zenith  distance,  were  recorded  simultane- 
ously with  the  indications  of  the  Secchi  instrument  furnished 


TUE   THERMOUELIOMETEB. 


257 


Table  A 

,    SHOWING 

TUE  Hesult  of  Observations  made  with 

Secchi's  Tiieumoheliometer, 

manufactured  by  Casella. 

SEPTEMBER  S. 

Ill 

External  casing. 

3i 
p 

if 

tS.a 

Upper 
thermometer. 

Lower 
thermometer. 

Mean. 

•F<A. 

•  Fa^. 

'Fah. 

'Fah. 

'Fah. 

Dtg. 

83.5 

j 

76.0 

70.0 

73.0 

10.5 

33.0 

84.2 

77.0 

71.5 

74.2 

10.0 

8.5.5 

70.0 

74.2 

76.6 

8.8 

32.50 

86.0 

83.5 

74.5 

79.0 

7.0 

89.0 

84.0 

75.5 

79.7 

9.2 

33.0 

90.5 

85.0 

76.5 

80.7 

9.7 

92.0 

85.5 

78.0 

81.7 

10.2 

33.10 

93.0 

86.5 

79.0 

82.7 

10.2 

94.0 

87.8 

80.0 

83.9 

10.1 

33.21 

94.5 

89.0 

81.5 

85.2 

9.2 

95.5 

90.0 

82.5 

86.2 

9.2 

33.32 

9G.5 

90.5 

83.5 

87.0 

9.5 

98.0 

91.5 

84.5 

88.0 

10.0 

33.44 

99.0 

92.0 

85.0 

88.5 

10.5 

100.0 

93.0 

80.0 

89.5 

10.5 

33.56 

101.0 

93.5 

86.5 

90.0 

11.0 

101.5 

94.0 

87.0 

00..-) 

11.0 

34.8 

93.1 

86.9 

79.7 

83.3 

9.80 

33.24 

a58 


BADIANT  HEAT. 


Table   B, 

SHOWING   THE    1!esult  of   Obskuvatioxs   -mape   with 

Secch] 

'S   TUEKMOIIELIO.METEH,    MANUFACTURED    BY    CaSELLA. 

SEPTEMBER  6. 

lis 

O    o    (D 

External  easing. 

3  2 

II 

^1 

Upper 
thermometer. 

Lower 
thermometer. 

Mean. 

°i?aA. 

'ITah,. 

'  Fah. 

"  Fah. 

"  Fah. 

Deg. 

94.0 

88.0 

81.5 

84.7 

9.7 

35.56 

95.5 

88.5 

83.0 

85.7 

9.7 

96.5 

89.5 

84. 5 

87.0 

9.5 

35.41 

97.5 

90.0 

85.0 

87.5 

10.0 

98.0 

90.0 

85.0 

87.5 

10.5 

35.26 

98.5 

90.5 

85.5 

88.0 

10.5 

99.0 

90.5 

85.7 

88.1 

10.9 

35.11 

100.0 

91.0 

86.5 

88.7 

11.2 

100.3 

91.0 

87.0 

89.0 

11.3 

34.56 

100.3 

91.2 

87.5 

89.3 

11.0 

100.5 

91.5 

88.0 

89.7 

10.8 

34.41 

98.2 

90.1 

85.3 

87.7 

10.45 

35.33 

SEPTEMBER  27. 

78.5 

64.0 

64.0 

64.0 

14.5 

44.0 

79.0 

65.0 

64.0 

64.5 

14.5 

79.5 

65.0 

64.5 

64.7 

14.7 

44.55 

79.5 

63.0 

65.0 

64.0 

15.5 

79.5 

64.0 

65.0 

64.5 

15.0 

45.51 

79.0 

64.5 

65.0 

64.7 

14.2 

79.0 

64.5 

65.5 

65.0 

14.0 

46.48 

79.0 

64.5 

65.5 

65.0 

14.0 

79.0 

65.0 

65.5 

65.2 

13.8 

47.46 

79.1 

64.4 

64.9 

64.65 

14.45 

45.16 

CUAI-.  XV.  lUE   TUEliMOUEl.lOMETEIi.  259 

by  Casella.  Let  us  fii-st  couskler  the  tabulated  observations 
of  September  2,  recorded  at  equal  intervals  of  three  minutes. 
The  indication  of  the  two  theruK)nieters  immersed  in  the 
tUiid  contained  in  the  annular  space  first  claims  our  attention, 
since  the  temperature  of  this  fluid  is  'the  principal  element  in 
Pere  Secchi's  original  computations  of  solar  temperature.  It 
will  be  seen,  on  referring  to  the  secimd  and  third  cohnnns  of 
the  table,  that,  while  the  upper  thermometer  indicates  a 
mean  temperature  of  SG^'.O,  the  lower  one  shows  only  79°.."), 
difference  =  7°.4.  This  great  discrepancy  of  temperature  at 
differeut  points  of  the  upper  portions  of  the  anmdar  space 
at  which,  owing  \.o  the  inclined  pt)sition  of  the  concentric 
tubes,  something  like  uniformity  ought  to  exist,  suggests  a 
still  gi'eater  discrepancy  of  temperature  at  the  under  side 
towards  the  lower  termination  of  the  tubes.  In  addition, 
therefore,  to  the  observed  irregularity  of  temperature  at  the 
upper  pai-t,  shown  by  the  table,  no  indication  whatever  is 
furnished  of  the  temperature  of  the  fluid  in  the  annular 
space  below  the  central  tube,  nor  towards  the  termination 
at  either  side.  Obviously,  then,  no  accurate  computation 
can  be  made  of  the  degree  of  refrigeration  to  which  the 
central  thermometer  is  exjoosed  by  the  radiation  from  the 
cold  Itlackened  surface  of  the  internal  tube,  every  part  of 
which,  as  we  have  seen,  possesses  a  different  temperature 
compared  A\ith  the  rest,  consequently  transmitting  radiant 
energj"  of  different  intensity.  It  will  be  found  practically 
impossible,  therefore,  to  detemiine  the  true  differential  tem- 
perature of  the   contents  of  the   bulb   exposed  to  the  sun's 


260  MADIANT  HEAT.  chap.  xv. 

rays  and  the  fluid  contained  in  the  annular  space.  Hence, 
the  differential  temperature  entered  in  the  table,  the  result 
of  comparing  the  indications  of  the  thermometers,  is  mani- 
festly incorrect.  It  will  be  found,  also,  by  reference  to 
Table  A,  that,  while  the  mean  temperature  imparted  to  the 
central  thermometer  by  the  sun's  rays  is  93°.  1,  the  mean 
temperature  of  the  fluid  in  the  annular  space  is  83°. 3.  Con- 
sequently, the  intensity  of  solar  radiation  established  by  the 
instrument  is  only  93°.l  —  83°.3  =  9°.80  F.  Now,  the  sun 
during  the  recorded  experiment  of  September  2  was  excep- 
tionally clear,  the  mean  indication  of  the  actinometer  while 
the  experiment  lasted   being  60°.05,    thus   sho\\ing   that  the 

energy  developed  was  only  — '- —  =  0.16  of  the  true  radiant 
^  "^    60.05 

intensity.  The  mean  zenith  distance,  it  may  be  mentioned, 
was  only  33  deg.  24  min.  during  the  exjieriment.  Agree- 
ably to  the  table  of  temperatures  (see  Chap.  III.),  the  maxi- 
mum solar  intensity  for  the  stated  zenith  distance  is  63°.35  ; 
thus  we  find  that  the  sun,  as  stated,  was  exceptionally  clear 
while  the  trial  took  place,  which  resulted  in  developing  the 
trifling  intensity  of  9°.80  F.  The  result  of  the  experiments 
conducted  September  6,  recorded  in  Table  B,  it  will  be 
seen,  was  nearly  the  same  as  that  just  referred  to,  the  mean 
temperature  indicated  by  the  thermometer  exposed  to  the 
sun  being  98°.2,  while  the  mean  of  the  two  thermometers 
immersed  in  the  fluid  was  87°.7 ;  hence  the  differential  tem- 
perature 98°.2  -  87°.7  =  10°.45.  The  mean  temperature  of 
solar   radiation    during    the    experiment,    ascertained   by   the 


CUAP.  XV.  TIU-:   TUEimOBELIOiLETHB.  261 

aotinometer,  was  5'J°.75,  the  zeuitb  distance  being  35  cleg.  33 

mill.     Consequently,  the  intensity  indicated  September  G  was 

^      10.45 
only  zrrzz  =  ^'-1"   of  the  true  enei'icy  of   the   sun's   radiant 

lu'at,  against  O.IG  during  the  previous  experiment.  It  will 
be  observed  that  the  fluctuation  of  the  differential  tempera- 
ture was  much  greater  SejJtenibcr  2  tliaa  duiiiig  the  succeed- 
ing experiment,  owing,  no  doubt,  to  the  influence  of  currents 
of  air  produced  by  a  strong  breeze  on  the  first  occasion,  the 
I'evolving  observatory  being  partially  open  on  the  side  pre- 
sented to  the  sun  during  observations. 

With  reference  to  the  small  differential  temperature  indi- 
cated by  the  Secchi  instniment  manufactured  by  Casella,  it 
may  be  urged  that  it  is  not  intended  to  sho\v  the  true  inten- 
sity of  solar  radiation  on  the  earth's  suiface,  but  simjjly  a 
means  of  deteiTuining  solar  temperature.  Granted  that  such 
is  the  object,  yet  the  extreme  irregularity  of  the  temperature 
of  the  fluid  within  the  aniuilar  space  shows  that  the  instru- 
ment is  unreliable — a  fact  established  beyond  contradiction 
by  an  experiment  instituted  September  27,  on  which  occasion 
water  of  a  uniform  temperature  was  circulated  through  the 
annular  space.  This  was  effected  by  gradually  charging  the 
intervening  space  from  the  top,  and  carrying  off  the  waste 
at  the  bottom,  holes  having  been  drilled  in  the  external 
casing  for  that  purpose.  The  result  of  this  conclusive  expe- 
riment is  recorded  at  the  foot  of  Table  B.  It  \vill  be  found, 
on  reference  to  the  figures,  that  the  mean  difference  of  the 
two  thermometers  immersed   in   the  fluid   was  only   64°.9  — 


262  EADIAM  MEAT.  chap.  xv. 

04:°.4  =  0.5°,  while  tlie  mean  differential  temperature  was 
augmented  to  79".!  —  64:°.65  =  14°.45,  against  9°.80  on  tlie 
:2nd  of  September,  althougli  the  zenitli  distance  was  greater, 
and  the  solar  intensity  less ;  circumstances  which  ought  to 
have  diminished  the  indicated  intensity.  It  is  needless  to 
enter  into  any  further  discussion  of  the  demerits  of  the 
instrument  represented  in  Fig.  2.  We  maj'  uo\v  return  to 
the  consideration  of  the  device  delineated  in  Fig.  1,  copied 
from  "  Le  Soleil."  It  will  be  seen  that  the  material  diffe- 
rence of  construction  is  that  of  applying  only  one  thermo- 
meter for  ascertaining  the  temperature  of  the  fluid  in  the 
annidar  space.  Possibly  this  single  thermometer  may  indi- 
cate approximately  the  mean  tempei'atui'e  of  the  uppei'  and 
lower  portions  of  the  fluid  above  the  central  tube  ;  but  it 
furnishes  no  indication  of  the  temperature  below,  nor  at 
either  extremity  of  the  annular  space.  The  iuaderpiacy  of 
the  means  adopted  for  ascertaining  the  temperature  of  the 
intei'nal  sui-face  which  radiates  towards  the  bulb  of  the  cen- 
tral thermometer  having  thus  been  pointed  out,  it  Mill  be 
well  to  consider  whether  the  expedient  of  passing  a  stream 
of  \vater  of  nearly  uniform  temperature  through  the  annular 
space  will  insure  trustworthy  indication.  In  order  to  deter- 
mine this  question,  I  have  constructed  two  instruments,  in 
strict  accordance  with  the  delineation  in  Fig.  1,  excepting 
that  in  one  of  these  the  concentric  cylinders  are  considerably 
enlarged,  the  annular  space,  however,  remaining  unchanged. 
Ex|ieriments  with  the  two  instruments  prove  that  the  enlarge- 
ment does  not  materially  influence  the  indications,  provided 


THE  THEBMOUELJOMETEIi. 


203 


Avatcr  of  a  uniform  teniperahue  be  circulated  tlirougli  the 
aiiiiuhir  hpacf.  But  tliese  exjicrinients  liave  deuioustiatcd 
that  the  size  of  tlie  Lull)  of  the  thcnnouieter  e.xpo.sed  to  the 


Table  C,  showing  the  Kesult  of  employing  diffehknt 

TlIEKVO- 

METEKS,    THE    Bvi.IIS   OF    WIIICI 

ARE   OF 

UNEQU. 

lL  Diam 

:ti:k. 

J) 

(tmctcr  of  B 

nib,  0.30 

Tmh. 

1  ij-iuch  tube. 

5S 

3-inch  tulie. 

c  2 

Siui. 

Fluid. 

Diff. 

Sun. 

Fluid. 

Diff. 

S!^ 

•Fah. 

'Fah. 

'Fah. 

Z)«(7. 

•Fah. 

'Fah. 

=  Fah. 

Dtg. 

74.0 

no.o 

14.0 

50.32 

77.5 

62.1 

15.4 

49.54 

74.5 

60.3 

14.2 

50.24 

78.5 

62.3 

16.2 

50.30 

75.0 

60.7 

14.3 

50.16 

79.0 

62.5 

16.5 

50.12 

75.5 

61.0 

14.4 

50.08 

79.0 

63.0 

IC.O 

50.21 

76.0 

61.0 

15.0 

50.01 

79.0 

63.0 

16.0 

50.30 

75.0 

60.6 

14.4 

50.16 

78.6 

62.6 

16.0 

50.12 

Ih 

<i meter  of  II 

idh,  0.58 

Inch. 

83.  C 

02.  G 

21.0 

49.54 

79.2 

CO.! 

19.1 

50.32 

85.5 

63.0 

22.5 

50.30 

81.0 

60.3 

20.7 

50.24 

8G.4 

63.4 

23.0 

50.12 

82.5 

60.7 

21.8 

50.16 

86.7 

63.5 

23.2 

50.21 

82.7 

60.7 

22.0 

50.08 

87.7 

63.7 

23.0 

50.30 

83.0 

61.0 

22.0 

50.01 

85.9 

63.2 

22.5 

50.12 

81.7 

60.6 

21.1 

50.16 

sun  cannot  lie  chauLicd  witliout  influencing  the  differential 
temperature  most  mateiially.  This  ^vill  be  seen  by  refer- 
ence to  Table  C\  uhicli   records    the    result    of   e.viierinients 


2(i4  RADIANT  HEAT.  chap.  xv. 

with  different  thermometers,  and  tubes  of  different  diameters, 
conducted  October  17.  As  on  previous  occasions,  the  instru- 
ments, in  order  to  insure  accurate  position,  were  attached  to 
the  deoliuation  table  arranged  within  the  revolving  observa- 
toiy.  The  bulbs  of  the  thermometers  employed  were  veiy 
nearly  sj^herical,  their  diameters  being  respectively  0.30  and 
0.58  inch.  The  upper  division  of  Table  C,  which  records  the 
experiment  with  the  small  bulb  exposed  to  the  sun,  estab- 
lishes, it  will  be  seen,  a  differential  temperature  of  14°.4 
for  the  instrament  having  the  Ij-in.  central  tube,  and  16° 
for  the  one  having  the  3-in.  central  tube.  Referring  to  the 
knver  division  of  the  same  table,  it  ^vill  be  seen  that,  Avhen 
the  thermometer  with  the  large  bulb  is  exposed  to  the  sun, 
the  differential  temperature  reaches  22°.5  in  the  instrument 
containing  the  \\-m  central  tube,  and  21°.l  in  the  one  having 
the  3-in.  tube.  We  thus  find  that,  by  doubling  the  diameter 
of  the  bulb  of  the  thermometer  exposed  to  the  sun,  all  other 
things  remaining  unchanged,  an  augmentation  of  the  differen- 
tial temperature  amounting  to  nearly  one-third  takes  place. 
This  fact  proves  the  existence  of  inherent  defects  fatal  to 
the  device  delineated  in  Fig.  1,  rendering  the  same  wholly 
unreliable. 

Agreeably  to  the  doctrine  of  exchanges,  the  diameter  of 
the  bid!)  is  an  element  of  no  moment,  since  the  internal  radi- 
ation towards  the  same — -jprovided  its  teinperature  he  nnifonn 
— depends  solely  on  the  temperature  and  angular  distances 
of  the  I'adiating  points  of  the  enclosure.  Infallibility  of  the 
thermoheliometer   has    evidently  been  taken   for   granted  on 


CHAP.  XV.  THE  TIIEBMOHELIOMETER.  205 

the  strength  of  the  suuiuluess  of  this  ductriue,  as  Ave  fiud 
no  allusion  to  the  size  of  the  bull)  in  M.  Soret's  account  of 
his  observations  of  solar  intensity  on  ]Mont  Blanc  ;  nor  does 
yiv.  AVaterston,  Avho  employed  a  similar  instrument  during 
his  obsei'vatious  in  India,  advert  to  the  dimensions  of  the 
bulb  of  the  thermometer  exposed  to  the  sun.  These  i>hysi- 
cists  apparently  overlook  the  fact  that,  ^vhile  the  entire  convex- 
area  of  the  bulb  is  exposed  to  what  may  be  considered  the  cold 
radiation  from  the  enclosure,  only  one-half  receives  radiant 
heat  from  the  sun.  This  circumstance  would  be  unimportant 
if  the  heat  thus  received  were  instantly  transmitted  to  every 
part ;  but  the  bulb  and  its  contents  are  slow  conductors, 
while  the  conducting  power  diminishes  nearly  in  the  iuvei-se 
ratio  of  the  square  of  the  depth.  Consequently,  by  increas- 
ing the  diameter,  the  parts  of  the  bulb  opposite  to  the  sun 
\\\\\  receive  considerably  less  heat  relatively  in  a  given  time 
than  if  the  diameter  be  diminished. 


CHAPTER   XVI. 


BAEOMETRIC    ACTINOMETEE. 


The  bulb  of  tlie  tLermometer  is  cliarged  mth  air ;  tlie 
intensity  of  the  radiant  heat  determined  by  the  pressure  in 
the  bulb  ;  the  height  of  the  mercurial  column  indicates  the 
pressure  ;  a  fixed  graduated  arc  and  movable  index  show  the 
sun's  zenith  distance  ;  the  graduation  of  the  scale  of  tempe- 
rature effected  without  exposing  the  bulb  to  heat  or  cold ; 
the  sun's  zenith  distance  and  the  intensity  of  the  i-adiant 
heat  observed  simultaneously  ;  the  bi;lb,  being  placed  within 
a  vacuum,  is  not  exposed  to  the  disturbing  influence  of  atmo-" 
spheric  currents ;  the  vessel  surrounding  the  bulb  maintained 
at  a  constant  temperature  ;  the  atmospheric  temperature  does 
not  affect  the  indication  of  radiant  intensity ;  the  quantity  of 
matter  contained  in  the  bulb  is  exceedingly  small  compared 
with  the  convex  area  exposed  to  the  solar  rays ;  suitable 
mechanism,  operated  by  two  small  hand-wheels,  enables  the 
observer  to  follow  the  diurnal  motion  and  sun's  declination  ; 
the  instrument  is  portable. 


cH.vr.  XVI.  BAUOMEIRIC  AVTlSOMETElt.  267 

Au  accurate  deteimiiiatioii  uf  the  iuteusity  of  solar  heat 
calls  for  a  thermoiueter  capable  of  indicating  the  temperature 
produced  by  radiation  after  a  very  brief  exposure  to  the 
radiant  heat.  It  has  been  pointed  out  in  previous  chapters 
that  the  sluggish  action  of  an  ordinary  thermometer  renders 
it  \\  holly  unfit  to  measure  the  temperature  produced  by  solar 
radiation  at  any  given  zenith  distance,  since  the  diurnal  motion 
is  so  rapid  that  before  an  equilibrium  can  be  established 
between  the  heat  received  by  the  bidb  and  the  heat  radiated 
by  the  same,  the  zenith  distance  is  materially  changed.  Con- 
sequently, the  temperatures  indicated  by  common  thermome- 
ter before  noon  are  too  low,  Avhile  in  the  afternoon  the  indi- 
cation is  too  high,  for  the  zenith  distance  at  any  given  instant 
of  time.  In  order  to  ascertain  to  \\\\i\i  extent  the  ordinaiy 
thermometer  is  defective  as  a  means  of  measuring  the  sun's 
radiant  heat,  consequent  on  the  slow  expansion  of  the  con- 
tents of  the  bulb,  I  have  conducted  a  series  of  experiments 
which  show  that  a  thermometer  surrounded  by  a  vessel  kept 
at  a  constant  temperature  and  exposed  to  the  i-adiation  of  a 
steady  gas-flame,  requires  from  20  to  25  minutes  before  the 
mercurial  column  becomes  stationaiy.  Consequently,  the 
rapid  change  of  the  sun's  zenith  distance,  especially  early 
in  the  morning  and  late  in  the  afternoon,  presents  a  difficulty 
which  renders  oidinary  theriuonieters  useless  for  measuring  the 
intensity  of  solar  heat  at  given  zenith  distances.  But  a  far 
greater  defect  inseparable  from  the  oidinaiy  form  of  thermo- 
meter remains  to  be  noticed,  namely :  the  section  of  the  pencil 
of  rays  which  imparts  the  radiant  heat  is  less  than  the  con- 


368  RADIANT  HEAT.  chap.  xvi. 

vex  area  of  the  bulb  exposed  to  tlie  sun.  This  circumstauce 
presents  a  serious  difficulty,  calling  for  delicate  counteracting 
expedients  (see  Chap.  III.),  since  although  that  half  of  the 
bulb  which  is  turned  away  from  the  sun  may  be  protected 
by  a  non-conducting  substance,  the  other  half  on  which  the 
sun  acts  exposes  a  radiating  surface  twice  as  great  as  the 
sectional  area  of  the  acting  pencil  of  I'ays,  because  the  convex 
area  of  the  bulb  is  four  times  greater  than  the  area  of  its 
greatest  section.  It  should  be  observed,  however,  that  by 
employing  a  long  bulb  of  cylindrical  form,  the  inherent  defect 
of  the  common  thermometer  thus  pointed  out  may  be  miti- 
gated in  the  ratio  of  about  4  to  3,  since  the  plane  which 
passes  through  the  axis  of  a  cylinder  bears  a  greater  pro- 
portion to  its  convex  area  than  the  area  of  the  great  circle 
of  a  sphere  to  its  convex  area.  Some  scientists  contend  that, 
agreeably  to  the  law  of  exchanges,  no  actual  loss  of  heat  is 
sustained  by  the  excess  of  radiating  surface  of  the  bulb  over 
the  sectional  area  of  the  pencil  of  I'ays  which  imparts  the 
radiant  heat.  A  moment's  consideration  will  dispose  of  this 
unsound  doctrine.  Admitting  that  by  means  of  non-conduct- 
ing substances  the  half  of  the  bulb  opposite  to  the  sim  may 
be  effectually  protected  against  loss  of  heat  by  radiation, 
the  other  half  which  is  turned  towards  the  luminary  will 
constitute  a  refrigerator  as  well  as  a  heater.  Now,  the  effi- 
ciency of  refrigerators  and  heaters  is  as  their  areas,  all  other 
things  being  alike  ;  hence  a  sj^herical  bulb  of  0.8  in.  diameter 
(the  convex  area  of  Avhich  is  2  square  inches)  presents  a 
radiating   surface    exactly    1    square    inch    towards    the    sun, 


CUA1-.  XVI.  BMlVMETiac  ACTIXOMETEE.  2G9 

while  the  section  of  tlie  peucil  of  tittlar  rays  Avliicli  the  bulb 
intercepts  contains  only  0.5  square  inch.  The  lays  lieing 
thus  distributed  over  an  area  twice  as  great  as  their  section, 
the  mean  intensity  of  the  radiant  heat  imparted  to  the  bulb 
will  be  diminished  one-half.  But,  while  the  hemispherical 
sui-face  of  the  IniUi  turned  towards  the  sun  is  thus  rendered 
inefficient  by  the  dispersion  of  the  rays,  its  efficiency  as  a 
vcfriyc-rato)',  remaining  unimpaired,  carries  off  the  lieat  with 
full  eneig}'  towards  the  surrounding  cold  medium.  As  our 
demonstration  relates  fmly  to  the  defect  consequent  on  the 
sectional  area  of  the  ])encil  of  rays  being  less  than  the  area 
which  receives  the  solar  heat,  I  have  not  noticed  the  serious 
loss  caused  by  cold  cun-ents  of  air  circulating  louud  the 
exposed  half  of  the  bulb.  The  self-evident  chai-acter  of  the 
foregoing  explanation  renders  theoretical  deductions,  from  the 
law  of  exchanges,  unnecessary  to  establish  the  fact  that  ordi- 
naiy  thermometei-s  cannot  furnish  correct  indications  of  the 
temperature  produced  by  solar  radiation. 

Before  entering  on  a  detailed  description  of  the  instru- 
ment illustrated  on  Plate  27,  it  will  be  instnictive  to  con- 
sider what  proportion  of  the  indicated  temperature  results 
from  vnaided  solar  Itcat  when  a  substance  surrounded  by 
the  atmosphere  is  exposed  to  the  sun's  rays ;  and  whether 
the  observed  increment  of  tenqierature  above  that  of  the 
suiTonnding  air  occupies  a  fixed  position  on  the  themio- 
metric  scale,  or  whether  it  rises  and  falls  with  the  inciease 
and  diminution  of  the  atmospheric  temperature.  Suppose 
that  we  place  a  circular  disc,  composed  of  some  black  non- 


270  BABIA^^T  HEAT.  chap.  xvi. 

conducting  substance,  at  the  bottom  of  a  veiy  deep  cyliu- 
di'ical  vessel,  kept  at  a  uniform  temperature,  ■whose  axis 
points  towards  the  sun,  and  "which  is  provided  "with  an  open- 
ing opjjosite  the  disc — the  diameter  of  the  disc  and  opening 
being  alike.  Suppose  also  that,  by  some  adequate  device, 
a  perfect  vacuum  is  kej^t  up  in  the  said  vessel,  and  that  the 
axis  of  the  black  circular  disc  is  directed  towards  the  solar 
centre.  I  maintain  that  the  temperature  acquired  by  the 
suiiace  of  the  supposed  disc — less  the  temperature  of  the 
surrounding  vessel — furnishes  an  accurate  indication  of  the 
real  intensity  of  the  sun's  radiant  heat.  It  will  be  perceived, 
on  due  reflection,  that  the  differential  temperature  thus  ascer- 
tained, which  furnishes  a  true  measure  of  the  I'adiant  inten- 
sity of  solar  heat,  cannot  occupy  a  fixed  position  on  the 
thermometric  scale.  It  rises  and  falls  by  increase  and  dimi- 
nution of  the  temperature  of  the  supposed  surrounding  vessel. 
The  investigations  and  observations  refei'red  to  in  Chap.  III., 
conducted  during  a  series  of  years,  it  should  be  borne  in 
mind,  have  established  the  fact  that  during  the  summer 
solstice  the  differential  temperature  produced  by  solar  radia- 
tion, indicated  by  my  actinometer,  is  fully  66°  F.  in  the 
latitude  of  New  York,  when  the  sky  is  perfectly  clear  and 
the  zenith  distance  18  degrees.  The  question  will  be  asked  : 
Is  there  any  limit  to  the  rise  and  fall  of  the  thermometric 
interval  of  66°,  consequent  on  changes  of  the  temperature 
of  the  surrounding  medium?  As  the  leading  j^oints  con- 
nected with  this  question  have  been  fully  discussed  in  Chap. 
IX.,  I  will  merely  observe  that  the  result  of  numerous  obser- 


CHAP.  XVI.  BAllOMETEIC  ACTINOMETEB.  271 

rations,  and  the  trial  of  various  expedients  resorted  to  in 
order  to  determine  the  limit,  show  that  the  movement  is  not 
limited.  The  extent  of  the  fall,  as  far  as  ascertained,  is  so 
considerable  that  Ave  must  infer  that,  but  for  the  intir\ention 
of  our  atmosphere  and  the  accumulation  of  heat  lesultinj^^ 
from  that  intervention,  the  sun's  unaided  radiant  heat  woidd 
not  be  sufficient  to  prevent  the  sui-face  of  the  earth  hum 
falling  several  hundred  degrees  below  the  freezing  point  of 
water.  No  reliable  experiments  have  yet  been  instituted  to 
ascertain  the  extent  of  the  upward  movement  of  the  thermo- 
metric  interval  under  discussion,  when  the  solar  rays  are 
admitted  into  an  incandescent  enclosure. 

The  following  general  description  will  enable  the  reader 
to  form  a  cori-ect  idea  of  the  nature  of  the  barometric  actino- 
meter.  The  leading  feature  of  the  instrument  is  that  of  em- 
ploying a  bulb  (see  Plate  27,  Fig.  1)  composed  of  very  thin, 
hard  plate-metal,  charged  with  dry  atmospheric  air,  in  place 
of  a  bulb  containing  some  liquid  substance.  The  lower  part 
of  this  air-bulb  is  heuiis^dierical,  Avhile  the  upper  part,  ex- 
posed to  the  sun,  consists  of  a  circular  plate  with  a  slight 
upward  curvature,  the  extreme  diameter  being  2.75  inches. 
The  hemispherical  jxirt  of  the  bulb  is  plated  with  nickel  on 
both  sides,  highly  polished  and  thoroughly  pi-otected  by  a 
non-conducting  external  covering,  A\"hile  the  t(->p  plate,  ex- 
posed to  the  radiant  heat,  is  coated  with  lampblack  on  the 
outside,  the  inside  presenting  a  rough  surface.  It  Avill  be 
evident  fi"om  this  description  that  the  form  of  the  bulb  of 
the  barometric  actinometer  fulfils   the   condition    inseparable 


273  FADIANT  HEAT.  chap.  xti. 

from  devices  intended  to  fumisli  accurate  indication  of  the 
intensity  of  solar  radiation — namely,  that  the  area  of  the  face 
Avliich  receives  the  radiant  heat  should  not  exceed  the  area 
of  the  section  of  the  pencil   of  rays  admitted  to  the  instru- 
ment.    The    air-bulb,  as    already   stated,   is   i^laced   near   the 
bottom   of    an    exhausted   cylindrical    vessel,    8    inches    long, 
3  inches  diameter,   surrounded    by  a    double   casing  through 
which   water,   kept  at  a  constant  temperature,  is    circulated. 
An     ordinary    force-pump    is     employed    for    this    purpose, 
receiving    its    supply    from    a    small    portable    cistern ;    the 
water    thus     circulated    through    the    double     casinij     beinff 
returned    to    the    c-istern    by   the    action    of   the    pump.     The 
upper  end  of  the  cylindrical  vessel  is  closed  by  a  plate  of 
glass   0.12  inch  thick,  forming  an  air-tight  joint.     Tlie  aper- 
ture in  the  ring  which   secures  the  glass  to  the  cylinder  is 
2.75  ins.  in   diameter,  corresponding  exactly  with  tliat  of  the 
bulb.     The  exhausted  vessel  is  held  in  position  by  a  trans- 
verse  axle   secured   to   its   bottom   (see   Fig.    2),   turning   in 
appropriate   bearings    supported   by  columns   resting   on    the 
circular    bed-plate   of  the    instrument.     The    transverse    axle 
mentioned  is  provided  with  a  central  perforation  ^vhich,  by 
means  of  minute  passages,  communicates  M'ith  the  interior  of 
the  bullj,  conmiunicating  also  with  a  close  mercurial  cistei-n  f 
formed  at  the  lower  end  of  the  barometric  tulje,  as  represented 
in  the  illustration.     The  height  of  the  column  in  this  baro- 
metric tube,  it  is  scarcely  necessary  to  observe,  furnishes  an 
exact  index  of  the  expansive  force  of  tlie  air  witliin  the  bulb, 
and  hence  the  intensity  of  the  radiant  heat  to  Avhich  it  is  sub- 


CHAP.  xvi.  BArxOMETBIC  ACTiyoMETER.  273 

jt'Cted.  It  is  iiiipoitiiiit  to  observe,  reganliiig  the  graduatiou 
of  the  scale  of  temperature,  that  the  height  of  the  mercurial 
column  alone  will  not  determine  the  length  of  the  degrees. 
Certain  obvious  corrections  must  be  made,  especially  on  ac- 
count of  the  loss  of  energy  of  the  sun's  radiant  heat  in 
passing  through  the  crystal  which  covers  the  exhausted  tube. 
This  loss  may  be  readily  ascertained  by  employing  an  appa- 
ratus by  means  of  which  the  absorptive  property  of  the 
crystal  is  tested  before  the  scale  of  temperature  is  graduated. 
Referring  to  the  mechanism  represented  in  the  illustration, 
it  will  be  seen  that  the  inclination  of  the  exhausted  cylin- 
der is  regulated  by  a  tangential  screw  a,  while  the  adjust- 
ment called  for  by  the  earth's  diurnal  motion  is  effected 
by  a  small  pinion  b  actuating  the  cogged  base-plate  which 
supports  the  instrument.  The  mechanism  thus  described, 
together  with  a  perforated  sight  c  and  an  index-plate  d, 
enables  the  operator  to  direct  the  tube  accurately  towards 
the  sun.  The  centre  line  of  the  index  (/  attached  to  the 
upper  end  of  the  exhausted  chamber  shows  the  zenith  dis- 
tance on  the  graduated  quadrant  at  all  times  by  raei'e  inspec- 
tion. It  should  be  mentioned  that,  when  the  barometric 
actinoiueter  is  arranged  within  a  revolving  observatory  pro- 
vided with  a  declination  table,  the  mechanism  just  described 
for  obtaining  a  parallactic  movement  is  wholly  dispensed 
^vith.  Meteorologists  will  do  well  to  adopt  such  an  insti-u- 
ment  in  all  important  observations,  since  its  simultaneous 
indication  of  solar  intensity  and  zenith  distance  enables  them 
to  determine   the   relative   amount    of  vapor  jiresent   in   the 


274  EADIANT  HEAT.  '        chap.  xvi. 

atmosphere  ^yith  a  degree  of  precision  probably  unattainable 
by  any  other  means.  The  sensitive  nature  of  the  instrument 
will  be  readily  comprehended  if  we  consider  that  while  the 
surface  of  the  bulb,  2.75  ins.  diameter,  amounts  to  5.93  square 
ins.  (the  section  of  the  pencil  of  rays  which  imparts  the 
radiant  heat  contains  also  5.93  superficial  inches),  the  quan- 
tity of  matter  to  be  heated  is  only  a  small  fraction  of  that 
contained  in  an  ordinary  thermometer  whose  bulb  is  only 
0.6  in.  diameter.  Besides,  the  latter  bulb  receives  heat  from 
a  pencil  of  rays  of  only  0.28  square  in.  section.  Apart  froni 
this  important  difference  in  favor  of  the  barometric  actino- 
meter,  the  radiating  surface  of  spherical  bulbs  exposed  to 
solar  radiation,  as  already  stated,  is  twice  as  great  as  the 
section  of  the  pencil  of  rays  Avhich  imparts  heat  to  the  same. 


CHAPTER  XVII. 


CONDUCTIVITY   OF  MERCURY. 


It  was  shown  in  Chapter  XV.  that  the  radiant  intensity 
of  the  sun  cannot  be  accurately  ascertained  by  the  thermo- 
heliometer  employed  by  Pere  Secchi,  owing,  among  other 
causes,  to  the  imperfect  conductivity  of  the  mercury  in  the 
bulb  exposed  to  the  sun.  ^leteorologists  are  not  generally 
aware  of  the  fact  that  the  conducting  power  of  mercuiy  is 
so  imperfect  as  to  affect  materially  the  correctness  of  the 
indication  of  mercurial  thermometei-s,  Deschanel  being  quoted 
in  support  of  the  opinion  that  mercury  is  a  very  good  con- 
ductor. Prof.  Everett,  in  a  recent  translation  of  the  works 
of  the  author  mentioned,  assumes  that  the  conductivity  of 
quicksilver  in  the  bulb  of  a  thermometer  is  the  same  as  a 
vessel  "  with  thin  metallic  sides  containing  water  which  is 
stirred"  (see  Prof.  Everett's  translation  of  "Deschanel's  Natu- 
ral Philosophy,"  Part  II.,  pp.  245-387).  The  subject  is  so 
intimately  connected  with  the  detennination  of  solar  tempe- 
rature   and    solar    energy   that    it    has    become    necessaiy    to 


276 


RADIANT  HEAT. 


CHAP.   XVII. 


settle  tbe  question  by  some  reliable,  practical  test.  I  have 
accortlingly  constructed  the  apparatus  illustrated  ou  Plate 
28,  by  means  of  wliicli  the  relative  conducting  j)ower  of  a 
colunm  of  copper  and  one  of  mercury  has  been  ascertained 
with  ci'itical  nicety.  Before  entering  on  a  description,  it  will 
be  instructive  to  point  out  that  the  heat  communicated  to 
the  bulb  of  a  thermometer  by  solar  radiation  is  transmitted 
to  its  contents  chiefly  by  convection;  hence  that  the  altitude 


of  the  sun  during  the  observation  influences  the  accuracy  of 
the  indication.  This  will  be  readily  comprehended.  Fig.  2 
represents  the  bulb  of  a  thermometer  exposed  to  the  rays 
Avhen  the  sun's  zenith  distance  is  65  deg. ;  Fig.  3  I'epresenting 
the  bulb  when  the  zenith  distance  is  18  deg.  23  min.,  the 
latter  being  the  minimum  at  the  observatory  of  the  Roman 
College,  where  the  thermoheliometer  described  in  Chajiter 
XV.  has  been  long  emjiloyed  for  the  purpose  of  ascertaining 


CHAP.  XVII.  COl^DUCTIVITY  OF  MEBCURT.  277 

the  inten.sity  of  solar  radiation.  Referring  to  Fig.  2,  it  will 
be  seen  that  the  blank  crescent  c,  whose  varying  thickness 
indicates  veiy  nearly  the  relative  amonnt  of  heat  imparted 
at  each  point  of  the  spherical  surface  pi-eseiited  towards  the 
sun,  occupies  an  almost  vertical  position.  The  mercury  con- 
tained within  the  space  indicati-d  by  the  said  crescent,  hav- 
ing its  specific  gravity  reduced  by  the  heat  transmitted  by 
the  solar  rays,  will  ascend  ;  w  hile  tlie  mercury  on  the  f)pposite 
side,  which  retains  its  specilic  gravity,  will  descend  ;  thus  a 
circulation  will  be  established  by  means  of  which  the  heat 
received  from  the  sun  will  be  gi'adually  communicated  to  the 
entire  mass  of  mercur}^  in  the  bulb.  But  when  the  latter 
is  exposed  to  the  sun's  rays  under  a  zenith  distance  of  about 
18  deg.,  as  shown  in  Fig.  3,  the  heated  mass  (jf  mercury  con- 
tained within  the  crescent  a  has  so  slight  an  im-lination  that 
scarcely  any  circulation  takes  place.  Consequently,  if  it  can 
be  sho\\Ti  practically  that  mercury  is  incapable  of  transmit- 
ting heat  from  particle  to  particle  with  sufficient  velocity, 
it  will  be  evident  that  thermometei's  and  thermoheliometers 
with  spherical  bulbs  are  worthless  as  means  of  measuring 
maximum  intensity  of  solar  radiation.  It  will  be  perceived 
that  if  the  bulb  in  Fig.  3  be  surrounded  by  an  enclosure,  as 
in  the  thei'iuoheliometer,  the  mercury  contained  witliin  the 
space  indicated  by  the  crescent  h  will  radiate  far  less  heat 
towards  such  enclosure  than  the  mercury  within  the  opposite 
heated  crescent  a.  It  will  also  be  perceived  that,  by  increas- 
ing the  size  of  the  bulb,  the  transmission  of  heat  from  a  to  h 
will  be  retarded  unless  the  conductivity  of  mei-cury  ]>e  pei-- 


278  RADIANT  HEAT.  chap.  xvii. 

feet.  Heuce  the  size  of  the  bulb  is  an  element  aflFecting  the 
accuracy  of  the  indication — a  circumstance  fatal  to  the  em- 
ployment of  a  sjiherical  bulb  in  the  thermoheliometer. 

The  nature  of  the  illustrated  apparatus  constructed  for 
the  determination  of  the  conductivity  of  mercury  will  be 
readily  understood  by  the  following  description:  Fig.  1, 
Plate  28,  represents  a  longitudinal  section  through  the  verti- 
cal plane,  a  is  a  boiler,  with  a  flat  bottom  and  semicircular 
ends,  supported  on  two  columns  /  and  g,  resting  on  the 
bottom  of  the  cisterns  c  and  d.  The  column  /  is  composed 
of  wrought  copper  plated  with  silver,  highly  polished.  The 
column  g  consists  of  a  cylindrical  vessel  of  glass  open  at 
the  top,  filled  with  mercury,  and  surrounded  with  a  socket 
h,  composed  of  polished  silver.  The  cisterns  c  and  d,  sup- 
ported on  non-conducting  substances,  are  plated  with  polished 
silver,  and  provided  with  funnel-shaped  openings  at  the  top, 
through  which  thermometers  are  inserted.  These  cisterns, 
as  well  as  the  columns  /  and  g,  are  surrounded  with  non- 
conducting coverings  j9,  ^p  and  o,  o.  A  lamp  h  is  applied 
between  the  cisterns  for  heating  the  water  in  the  boiler.  It 
is  scarcely  necessary  to  observe  that  the  polished  silver  plat- 
ing of  the  copper  column,  and  the  polished  silver  socket 
round  the  mercurial  column,  are  intended  to  prevent  loss  of 
heat  by  I'adiatitm,  while  the  coverings  before  mentioned  are 
intended  to  prevent  loss  of  heat  by  convection  attending 
atmospheric  currents.  The  inside  diameter  of  the  cylindrical 
vessel  g,  it  should  be  noticed,  is  0.5  in.,  corresponding  exactly 
with  the  diameter  of  the  copper  column  f,  the  top  of  which 


CHAP.  XVII.  COXDVCTIVITT  OF  MEBVUEY.  279 

is  on  a  level  with  that  of  the  mercurial  column.  The  lines 
Ic  I  and  m  n  are  in  the  same  horizontal  plane,  their  distance 
below  the  upper  ends  of  the  columns  /  and  g  being  precisely 
2  inches. 

The  object  of  the  apparatus  being  that  of  comparing  the 
conductivity  of  mercuiy  to  that  of  some  other  metal,  copper 
has  been  selected,  as  its  conducting  property  is  better  known 
than  that  of  any  other.  The  leading  feature  of  the  arrange- 
ment will  be  comprehended  by  a  mere  glance  at  the  illustra- 
tion. An  equal  amount  of  heat  being  applied  to  the  top  of 
each  column,  it  is  intended  to  show  by  the  elevation  of  the 
temperature  of  the  water  in  the  cisterns  c  and  d  what  rela- 
tion exists  between  the  conductivity  of  mercury  and  copper. 
Regarding  the  application  of  the  heat,  it  will  be  evident  that 
an  equal  amount  must  infallibly  be  imparted  to  each  column 
if  the  lamp  be  sufficiently  powerful  to  keep  the  water  in  a 
state  of  continuous  ebullition.  Obviously  the  heat  from  the 
lamp,  if  urged,  will  cause  a  rapid  upward  motion  of  the 
water  in  the  middle  of  the  boiler,  and  a  correspondingly 
rapid  descending  current  at  each  end.  Accordingly,  lateral 
currents,  varpng  in  velocity  with  the  strength  of  the  flame, 
applied  under  the  boiler,  mil  fl.ow  inwards  over  the  upper 
ends  of  the  columns  /  and  g. 

Several  experiments  have  been  made  under  different  baro- 
metric pressure  and  different  atmospheric  temperature,  yet 
the  results  as  regards  the  comparative  conductivity  of  mer- 
cuiy and  copper  have  proved  to  be  very  nearly  alike  in  all. 
The  accompanying  tables  record  the  result  of  the  last  trial, 


380 


BADIANT  HEAT. 


CHAP.  XVII. 


Table  I. — Coppeb  Column. 

'^ 

A 

n 

o 

.3 

±3 

^a  C 

o 

J^      ® 

6 

3  ^  S 

35  a 

0J«  3 

tec— 

s 

a   .s 

gjS. 

til 

H 

o 

1 

1      ' 

1      ^ 

Min. 

'Fah. 

°Fah. 

Therm,  mitts. 

°J?aA. 

Therm,  units. 

TAerm.  uni^. 

73.50 

138.50 

0.5 

75.15 

1.65 

0.143 

136.85 

0.143 

104.873 

1.0 

77.25 

3.75 

0.326 

134.75 

0.183 

134.208 

1.5 

80.14 

6.64 

0.577 

131.80 

0.251 

184.078 

2.0 

83.84 

10.34 

0.898 

128.10 

0.321 

235.415 

2.5 

88.14 

14.64 

1.272 

123.80 

0.374 

274.284 

3.0 

92.81 

19.31 

1.678 

119.00 

0.406 

297.752 

3.5 

97.67 

24.17 

2.100 

114.25 

0.422 

309.486 

4.0 

102.56 

29.06 

2.525 

109.44 

0.425 

311.686 

Table  II 

. — Mercurial  Column. 

H 

.3 
0  3   • 

a  a  " 
«_2 

1 
i  s 
If 

be  A 

III 

Si 

r3 

IS 
1  ^ 

^3 

c    .'c 

Min. 

°J?'aA. 

°^aA. 

Therm.  «»j's. 

-  /'-a/i. 

T/ierm.  units. 

T/ierm.  units. 

73.50 

138.50 

0.5 

73.52 

0.02 

0.002 

138.48 

0.002 

1.466 

1.0 

73.56 

0.06 

0.005 

138.44 

0.003 

2.200 

1.5 

73.64 

0.14 

0.012 

138.36 

0.007 

5.133 

2.0 

73.75 

0.25 

0.022 

138.25 

0.010 

7.334 

2.5 

73.90 

0.40 

0.035 

138.10 

0.013 

9.534 

3.0 

74.08 

0.58 

0.051 

137.92 

0.016 

11.734 

3.5 

74.28 

0.78 

0.068 

137.72 

0.017 

12.467 

4.0 

74.50 

1.00 

0.087 

137.50 

0.019 

13.934 

CHAP.  XVII.  COXDUCTIVITY  OF  MEUCUUY.  .  281 

comlucted  as  carefully  as  practicable.  The  lieailiiigs  of  the 
several  columus  explain  so  clearly  the  object  of  the  tables 
that  it  will  only  be  necessary  to  ^ate  that  the  energy  in- 
serted iu  the  fourth  column  is  the  energy  developed  from  the 
beginning  of  the  experiment 

Referring  to  Table  I.,  it  will  be  seen  that  at  the  termina- 
tion of  4  minutes  from  the  commencement  of  the  experiment, 
the  temperature  of  the  water  in  the  cistern  v  bad  increased 
29'.0G,  the  differential  temperature  being  then  212°  -  102°.56 
=  109°.44  F.  During  the  same  period  an  amount  of  dynamic 
enero-y  represented  by  2.525  thermal  units  had  been  trans- 
mitted past  the  line  l  1,  communicated  to  (1)  the  water  in 
the  cistern ;  (2)  the  part  of  the  copper  column  immersed  ; 
(3)  the  metal  composing  the  cistern ;  (4)  the  immersed  part 
of  the  thermometer.  But,  while  the  entire  energy  transmitted 
past  the  line  I-  I  during  the  4  minutes  thus  amounted  to  2.52.3 
units,  the  rate  of  transmission  was  actually  0.850  unit  per 
minute  at  the  termination  of  the  fourth  minute.  This  appa- 
rent discrej>ancy  was  caused  by  the  heat  absorbed  Ijy  that 
part  of  the  column  which  extends  above  the  line  h  I,  the 
temperature  at  the  commencement  of  the  experiment  being 
the  same  as  that  of  the  surrounding  air,  73'.50.  Referring 
to  Table  II.,  it  will  be  seen  that  the  euerg>=-  transmitted 
through  the  mercurial  column  past  the  line  m  n,  during  4 
minutes,  was  only  0.087  unit  against  2.525  units  for  the 
copper  column,  although  the  differential  temperatui-e  of  the 
water  in  the  cistern  ^^  was  137°.50  -  109'.44  =  28^06  higher 
than  in  the  cistern  c.     Accordingly,  the  conductivity  of  the 


282  RADIANT  HEAT.  chap.  xvii. 

2.526 
copper  composing  the  column  /'  has   proved  to  be  ;:  = 

29.06  times  greater  than  the  conductivity  of  tlie  mercury  of 
the  column  g,  notwithstanding  the  higher  differential  tempe- 
rature to  which  the  latter  was  exposed.  It  will  be  observed 
that  the  glass,  0.02  in.  thick,  composing  the  cylindrical  vessel 
which  contains  the  mercury,  will  conduct  some  heat  down- 
ward, tending  to  increase  the  temperature  in  the  cistern  d. 
This  tendency,  however,  will  be  balanced  by  the  loss  of 
heat  occasioned  by  the  radiation  of  the  glass  cylinder,  since 
the  application  of  the  polished  silver  socket  and  the  non- 
conducting covering  cannot  wholly  prevent  the  refrigerating 
action  of  the  surrounding  air.  It  is  important  to  observe, 
regarding  the  loss  of  heat  from  the  latter  cause,  that  the  cis- 
terns, previous  to  trial,  are  charged  with  water  of  the  same 
temperature  as  the  atmosphere.  No\v,  considering  that  the 
increment  of  temperature  in  the  cistern  d  does  not  averao-e 
more  than  0°.40  above  that  of  the  atmosphere  during  the 
trial,  it  will  be  evident  that  the  amount  of  error  caused  by 
radiation  will  be  quite  inappreciable.  We  are  therefore 
warranted  in  concluding  that  the  conductivity  of  mercury, 
determined  by  the  increment  of  temperature  in  cistern  d, 
and  by  the  dynamic  energy  transmitted  past  the  line  m  n, 
cannot  be  far  from  correct.  It  will  be  asked  why  columns 
of  such  small  diameter  have  been  employed.  The  principal 
object  has  been  that  of  presenting  a  sectional  area  in  the 
mercurial  column  g  corresponding  as  nearly  as  possible  to 
the  size  of  the  bulb  of  an  ordinary  thermometer.     The  inves- 


CHAP.  XVII.  COi\J)VCTIViri'  OF  MEIiCVliY.  283 

tigation,  then,  has  couclu.sively  established  the  fact  that  mer- 
cury transmits  heat  from  particle  to  particle  too  slowly  to 
effect  a  sufficiently  rapid  indication  of  mercurial  thermome- 
ters provided  with  splierical  bulbs ;  and  that,  when  the  heat 
is  applied  from  above,  the  indication  of  such  thermometers 
is  wholly  um'eliable. 

A  subject  of  great  interest  presents  itself  in  connection 
with  the  rate  of  transmission  of  energy  exhibited  in  the 
sixth  column  of  Table  I.  It  will  be  seen  that,  although  the 
copper  column  /  is  only  0.5  in.  in  diameter  =  0.19635  sq.  in. 
section,  the  rate  of  transmission  at  the  termination  of  the 
fourth  minute  is  0.850  unit  per  minute.  Reducing  this 
amount  to  the  usual  standard  of  one  square  foot,  it  will  be 

144 

found  that  the  energy  developed  is   X  0.850  =  623 

"'•'  ^  0.19635 

thermal  units  per  minute  for  a  sectional  area  of  one  square 

foot.     It  will  be  observed  that  this  extraordinary  amount  of 

•     ,,  ,,        .  .623 

energy  (theoretically  capable  of  exerting  =  14.5   horse- 

42.7 

power)  is  called  forth  by  the  moderate  differential  tempera- 
ture of  212°  -  102°.56  =  109°.44  F.  Now,  let  us  compare 
the  stated  energy  of  623  thermal  units  per  minute  to  that 
produced  by  the  radiation  of  a  metallic  surface  coated  with 
lamp-black,  and  maintained  at  a  temperature  of  212"  within 
an  enclosure  of  102^  Actual  trial  shows  that,  under  these 
conditions,  the  radiant  energy  emanating  from  the  face  of  a 
plate  composed  of  copper,  containing  144  sq.  ins.,  scarcely 
reaches  6  theraial   units   per   minute.      Our   experiment   has 


284  BABIANT  HEAT.  chap.  xvir. 

therefore  incidentally  established  the  fact  that,  under  the 
stated  conditions,  a  plate  of  wrought  copper  2  ins.  in  thick- 
ness is  capable  of  transmitting  by  conduction  from  one  side 
to  the  other,  in  a  given  time,  an  amount  of  mechanical  energy 
more  than  one  huntlred  times  greater  than  the  mechanical 
energy  transmitted  by  the  radiation  of  the  same  plate  during 
an  equal  interval  of  time. 


CHAPTER  XYIII. 


INCANDESCENT  CONCAVE  SPHEPJCAL  HADIATOK. 


The  illustration  on  Plate  29  represents  an  apparatus 
constructed  for  the  purpose  of  j^roving  the  correctness  of 
the  indications  furnished  by  the  solar  pyrometer  described 
in  Chapter  X.  Fig.  1  is  a  side  elevation  and  Fig.  2  an 
end  view  of  the  apparatus.  Objections  have  been  raised 
against  the  solar  pyrometer  on  account  of  the  low  tempera- 
ture employed.  It  is  contended  that,  unless  the  radiator  is 
raised  to  the  temperature  of  incandescence,  emitting  luminous 
rays,  the  radiant  heat  transmitted  to  the  focus  will  not  fui'- 
nish  an  indication  capable  of  determining  the  temperatui-e 
of  distant  incandescent  bodies.  The  reader  is  aware  that 
the  idea  of  ascertaining  the  temperature  of  the  sun  by  the 
indications  of  a  surface  coated  with  lamp-black,  maintained 
at  only  boiling  heat,  has  lieen  deemed  absurd  by  certain 
pliysicists.  Secchi,  in  a  letter  to  Nature,  says :  "  Very  few 
indeed  \vill  allow  tliat  which  ]Mr.  Ericsson  takes  for  granted, 
that  the  radiating  power  of  the  solar  materials  may  be  com- 

3^ 


286  RADIANT  HEAT.  chap,  xviii. 

pared  to  tLat  of  pure  lamj^-black,  as  lie  assumes."  Numerous 
experiments,  lio\vever,  sliow  tliat,  relatively,  there  is  no  appre- 
ciable difference  between  tlie  energy  of  the  dark  heat-rays 
emanating  from  a  metallic  radiator  of  low  temperature,  pre- 
senting a  thoroughly  disintegrated  or  a  blackened  surface, 
and  the  energy  of  heat-rays  accompanied  by  a  light  emanat- 
ing from  an  incandescent  metallic  radiator.  The  temperature 
transmitted  by  the  radiant  heat  to  the  focus  is,  in  each  case, 
directly  proportional  to  the  temperature  of  the  radiant  sur- 
face. An  air  thermometer  placed  in  the  focus  of  a  concave 
spherical  radiator  composed  of  ice,  and  surrounded  with  very 
cold  substances,  say  100°  below  zero,  will  furnish  an  indica- 
tion by  which  the  temj^erature  of  distant  incandescent  bodies 
may  be  ascertained  with  as  much  certainty  as  by  employing 
a  radiator  heated  to  such  a  degree  as  to  emit  luminous  rays. 
It  scarcely  needs  explanation  that  my  reason  for  constructing 
the  solar  pyrometer  with  a  radiator  kept  at  the  low  tempe- 
rature of  boiling  water  is  that  of  admitting  of  operating 
within  a  vacuum,  besides  rendering  it  possible  to  measure 
the  temjjeratures  with  positive  exactness.  No  doubt  the 
instrument  could  be  so  arranged  that  the  metallic  radiator 
might  be  maintained  at  a  temperature  considerably  above 
that  of  incandescence  (Sir  Humphry  Davy,  it  will  be  remem- 
bered, fixed  the  temperature  of  incandescence  at  812°);  but 
we  lack  accurate  means  of  measuring  the  intensity  when 
metals  are  brought  to  white  heat  or  bright  orange.  Nor 
would  anything  be  gained  by  resorting  to  a  mode  of  con- 
struction involving  both  complication  and   uncertainty,  since 


UHAI-.  xviii.     INCANDESCENT  SPHERIOAL  RADIATOR.  287 

(laik  heat-rays,  with  refereuce  to  temperature,  in  no  manner 
differ  fi'oni  heat-rays  accompanied  by  light.  As  already 
stated,  no  irregularity  h;is  been  observed  by  me  in  the  fall 
of  the  temperature  of  an  incandescent  radiator,  and  that  of 
the  focal  thermometer  exposed  to  the  I'adiaut  heat,  while  the 
color  gradually  changes  fx'om  bright  orange  to  black.  On 
the  contrary,  the  temperatures  of  the  radiator,  and  the  reci- 
pient of  the  radiant  heat,  continue  to  bear  the  same  relation 
to  each  other  during  both  cooling  and  heating.  The  times, 
compared  mth  the  increment  or  diminution  of  intensity, 
differ  a  little;  but,  as  stated,  the  proportion  between  the 
temperature  of  the  radiant  surface  and  that  transmitted  to 
the  focus  continues  as  nearly  uniform  as  practical  test  can 
show. 

The  radiator  of  the  instrument  represented  by  our  illus- 
tration on  PI.  29  consists  of  a  solid  cylindrical  block  h,  com- 
posed of  cast  iron,  10  ins.  diameter,  6  ins.  long,  placed  hori- 
zontally on  a  pedestal,  the  fi-ont  end  forming  a  spherical 
concavity  a  h  c  of  18  ins.  radius,  precisely  like  the  radiator 
of  the  solar  pyrometer  described  in  Chap.  X.  The  under  side 
of  the  cylindrical  block  is  provided  with  a  square  projection 
corresponding  with  two  guide  pieces  on  the  top  of  the 
pedestal  shown  on  Fig.  2,  intended  to  facilitate  the  operation 
of  placing  the  block  rapidly  in  a  proper  position  after  having 
been  heated  in  an  aii--furnace.  A  focal  thermometer  J,  simi- 
lar to  the  one  employed  in  the  solar  pyrometer,  is  secured 
to  a  bent  arm  attached  to  the  front  side  of  the  pedestal ; 
the  distance  b  cl  between  the  centre  of  the  bulb  and  the  face 


BABJANT  HEAT. 


CHAP.   XVIII. 


a  b  c  oi  the  concave  spherical  radiator  being  also  precisely 
as  in  the  sohar  p}'rometer. 

The  accouipauyiug  table  exhibits  the  result  of  a  trial  of 
the  ajjparatus,  conducted  at  a  mechanical  establishment  in 
New  York  possessing  air-furnaces  well  adapted  for  the  in- 
vestia:ation : 


Appearance  of 
radiator. 

Temperature  of  radiator. 

is, 

<l-2 

Temperature  of  focal 
thermometer. 

Actual. 

Diflerential. 

Actual. 

Differential. 

'  Fah. 

°  Fah. 

°  Fah. 

°  Fah. 

'Fah. 

Light  orange.... 

Deej)  orange 

Br't  cherry  red.. 
Pull  cherry  red. 
Dull  cherry  red. 
Dull  red  heat. . . . 

Mean 

2190 

2010 
1830 
1650 
1470 
1290 

2149.3 
1969.3 
1789.3 
1609.5 
1429.8 
1249.0 

40.7 
40.7 
40.7 
40.5 
40.2 
41.0 

178 
173 
166 
150 
144 
130 

137.3 
132.3 
125.3 
115.5 
103.8 
89.0 

1740 

1699.87 

40.63 

157.83 

117.2 

The  following  brief  account  of  the  manner  of  conducting 
the  trial  \vill  show  the  simple  nature  of  the  investigation. 
Tlie  solid  radiator,  Ijefore  being  2)laced  on  the  pedestal,  Mas 
heated  in  the  air-furnace  to  very  nearly  white  heat,  and 
then,  by  means  of  tongs,  quickly  removed  from  the  furnace 
and  placed  in  the  position  shown  by  the  illustration.  The 
focal  thermometer  was  then  closely  observed,  its  indication 
being  recorded  when  the  radiator  had  cooled  so  as  to  pre- 
sent a  color  of  light  orange.  The  indications  during  the 
succeeding  stages  of  brightness  and  color  of  the  incandescent 


ciiAi'.  Win.     Ii\CAM)J-:SCEM  l^U'llKlilCAL   RMHATOR.  280 

radiator  were  in  like   iiiaiiucr  iveoi'ded.     The  teiiipeniture  of 

the  sui'rouucling  air   \\as>  observed    siiniiltaiieously   with   that 

of  the  focal  thermoiuetei'.     The  time  Avhich  elapsed  between 

tlie    fii'st   and   last   observation  entered    in    the    table    was   29 

minutes.     It  will   be  seen  that    the    temperature   transmitted 

by  the    radiator   to    tLe   focal   thermometer  was    recoi'ded  at 

six  different  stages  of  incandescence,  the   color  presented   by 

the    radiant    surface    determining    the    time    foi'    olxservation. 

The  mean  temperature  of  the  radiator  during  the  experiment 

was  1,740°  F.     Deducting  the  mean  atmospheric  temperature, 

40°. 63   F.,  the   actual   mean   differential   temperature   of  the 

radiant   surface,  the  lumint)us    heat   rays  of  ^vhicll  acted   on 

the  focal  thermometer,  was  1,699°.37.     The  mean  temperature 

transmitted  to  the  focal  thermometer  exposed  to  the  radiant 

heat   being   157°.83,   while   the   atmospheric   temperature,   as 

already   stated,    was    40°.63,   we    find    that    a    temperature  of 

117°.2  was  imparted  to  the  focal  thermometer  by  a  radiant 

intensity  of    1,699°. 37.     It   will   be    recollected    that    in   the 

solar   pyrometer   a   differential    radiant    intensity    of    163°.9 

transmitted  a  temperature  of  12°.2  to  the  focal  thermometer; 

12°.2 
hence  ■  =  0.074  of   the  temperature  of  the  i-adiator  was 

1 63.9 

117.2 
transmitted  to  its  focus,  against  ^^^j^jT^r;:  =  0.069    in    the    ap- 

paratus  under  consideration.  Conse([uently,  0.074  —  0.06i* 
=  0.00.5  less  heat,  relatively,  is  transmitted  by  the  incan- 
descent radiator  than  by  the  comparatively  cool  radiator  of 
the  solar  pyi'ometer.  As  this  small  discrepancy  can  readily 
be  accounted  for,  the  result  of  the  instituted  test  fully  estab- 


290  BABIANT  HEAT.  chap,  xvili. 

lislies  the  truth  of  the  doctrine  which  forms  the  basis  of 
the  sohu-  pyrometer — namely,  that  the  cakirific  energy  of  both 
dark  and  luminous  heat  rays  is  directly  proportional  to  the 
temperature  of  the  radiant  surface.  The  cause  of  the  dis- 
crepancy adverted  to  will  be  readily  comprehended  by  the 
following  explanation  relating  to  the  solar  pyrometer.  The 
heat  imparted  by  the  radiant  to  the  recipient  surface  is 
transmitted  through  ether  alone;  therefore  neither  the  radi- 
ator nor  the  bulb  of  tlie  focal  thermometer  are  subjected  to 
any  loss  by  convection ;  while  the  incandescent  concave  radi- 
ator, as  well  as  its  focal  thermometer,  are  exposed  to  the 
refrigerating  influence  of  the  atmospheric  air.  Obviously 
the  heated  bulb  of  the  thermometer  will  caiise  an  up^vard 
curi'ent  of  air,  which,  acting  on  its  face,  reduces  its  tempe- 
rature and  indication,  while  the  intense  heat  of  the  radiator 
tends  to  augment  the  said  current.  Again,  the  rapid  suc- 
cession of  cold  particles  passing  over  the  intensely  heated 
surface  of  the  radiator  will  inevitably  diminish  the  energy 
of  the  radiant  heat,  since  the  molecular  motion  within  the 
heated  mass  cannot  instantly  restore  the  loss  to  which  the 
molecules  at  the  siirface  are  continually  l:)eing  subjected  by 
the  cold  current.  The  diminution  of  radiant  energy  from 
this  cause,  though  not  great,  will  be  appreciable,  and,  added 
to  the  loss  of  heat,  to  which  the  bulb  of  the  focal  thermo- 
meter is  subjected,  satisfactorily  accounts  for  the  discrepancy 
adverted  to;  at  the  same  time  showing  the  necessity  of 
carrying  on  investigations  relating  to  radiant  heat  within  a 
vacuum. 


CHAP.  XVIII.     IXCAXl>i:SCi:XT  arJlERICAL   RADIATOn.  291 

Let  us  now  calculate  the  temperature  of  the  sun  agree- 
ably to  the  indications  furnished  by  the  incandescent  ladiatov 
of  the  illustrated  apparatus,  without  reference  to  the  iiidica- 
tioiis  of  tlie  iiistrunu'iit,  tlio  relialjility  of  wliicli  we  are  dis- 
cussing. But  in  place  of  basing  our  calculations  on  the 
angle  subtended  by  the  sun  from  the  earth,  and  the  angle 
subtended  by  the  concave  spherical  radiator  from  its  focus, 
let  us  detenniiie  tlie  solar  tennuTature  ou  the  basis  of  areas 
and  distances  alone.  This  method  will  be  more  satisfactory 
to  practical  men  than  the  one  which  takes  no  direct  cogni- 
zance of  areas  and  distances.  Assuming  the  sun's  diametei' 
to  be  852,584  miles,  the  area  of  the  great  circle  will  be 
15,912,029  X  10"  sq.  ft.  The  diameter  of  the  spherical  radi- 
ator being  10  ins.  and  the  radius  18  ins.,  its  face  presents 
80.06  sq.  ins.  =  0.556  sq.  ft.  Accoi'dingly,  the  sun's  area 
is  28,620,377  X  10"  times  greater  than  the  area  of  the  con- 
cave face  of  the  radiator.  The  mean  distance  between  the 
sun  and  the  earth  is  91,430,000  miles,  or  482,750,400,000  ft. ; 
the  distance  between  the  radiator  and  its  focus  is  1.5  ft. 
The  radiant  heat  of  the  sun,  theiefore,  acts  through  a  dl.s- 
tance  321,833,600,000  times  greater  than  the  radiant  heat 
of  the  incandescent  radiator.  We  have  demonstrated  in 
Chap.  I.  that  the  temperature  transmitted  to  the  foci  of 
concave  spherical  radiators  of  equal  area  is  inversely  as  the 
square  of  their  radii ;  and  we  have  sho\vn  that,  owing  to 
the  great  distance  of  the  sun,  every  part  of  his  face  may, 
without  material  error  in  our  computations,  be  considered  as 
equidistant  fi-oni  the  earth.     Hence,  if  we  square  and  invert 


292  BABIANT  HEAT. 


CHAP,  xvrii. 


the  lief  ore-mentioned  distances  tbrongli  whicli  the  I'.-idiant 
heat  acts,  we  ascertain  that  for  equal  intensity  and  equal 
area  the  incandescent  radiator  will  transmit  10;^, 57(5,800  X 
10"  times  higher  temperature  to  its  focus  than  that  trans- 
mitted by  the  sun  to  the  Iwundary  of  the  earth's  atmosphere. 
But  the  area  of  the  sun,  as  we  have  stated,  is  28,620,377  X 
10"  times  greater  than  the  area  of  the  radiator;  hence  for 
equal  inlensity  the  radiant  heat  transmitted  to  the  focus  of 

.      ,  ^^         .,,  -      103,576,866  X  10" 

the  latter  will  be    ^.^         '^^^   ^  ^^^,.,  =  3,618.99  times  greater 
28,620,3vY    X  10  ° 

than  that  transmitted  by  the  sun.     It  will   be  readily  seen, 

on    reflection,    that    unless    the    temperature    of    the    sun    is 

3,018.99  times  greater  than  that  of  the  incandescent  radiator, 

it   cannot   transmit   to   the    atmospheric    boundary   the   same 

temperature  as  that  transmitted  by  the  radiator  to  its  focus, 

viz.,  117°.2  F.     The  temperature  produced  by  solar  radiation 

when  the  earth    is    in    aphelion   is,  however,  only    84°.84:    at 

the   said   boundary;    hence   the    sun's    temperature    need    be 

,      3,618.99  X  84.84 

onlv   — — =  2,619.25  times  greater  than  that  of 

117.2  ^ 

the   incandescent    radiator  (1,099°.37),   in  order  to  cause    an 

elevation  of  84°.84  on  the  Fahrenheit  scale  at  the  boundary 

of  the  earth's  atmosphere.     Multiplying  1,099°.37  by  2,619.25, 

we    find    that    the    indication    of    the    incandescent    concave 

spherical  radiator  of  our  illustrated  device  proves  the  sun's 

temperatxire  to  be  4,451,924°  F.     It  will  be  seen,  on  referi-ing 

to  Chap.   X.,  that  the  calculations  based  on  the  indications 

of   the   solar   pyrometer   prove   the    sun's   temjserature  to  be 


cnAP.  XVIII.     TNCJXPESCEyT  SriTEHICAL  HADTATOn.  293 

only  4,063,984\  The  cause  of  this  discrepancy  of  0.087  has 
already  been  explained,  viz.,  diminution  of  the  radiant  energy 
of  the  incandescent  radiator,  produced  by  currents  of  cold 
air  sweeping  over  its  face  ;  together  with  the  loss  of  heat 
to  wJiich  the  unprotected  bulb  of  the  focal  therinonieter  is 
subjected  by  the  refrigerating  effect  of  the  surrounding  at- 
mosphere. Making  due  allowances  for  these  losses — insepa- 
i-al)le  from  conducting  the  e.xpei'inient  in  the  presence  of 
atmospheric  influence — it  will  be  found  that  the  indications 
furnished  by  an  incandescent  concave  spherical  radiator 
assign  very  iieaily  the  same  temperature  to  the  sun  as  the 
comparatively  cold  radiator  of  the  solar  pyrometer.  The 
objection,  then,  urged  against  this  instrument,  that  its  tem- 
jterature  is  not  high  enough,  cannot  be  maintained  in  view 
of  the  fact  which  we  have  established,  that  the  intensity 
deduced  from  its  indication  is  not  att'ected  by  employing  an 
incandescent  radiator  in  place  of  one  raised  to  merely  boiling 
heat. 


CHAPTER   XIX. 

REFLECTIVE  POWER  OF  SILVER  AND  OTHER  METALS. 


Desciianel  informs  us  that  the  reflection  of  calorific  rays 
has  been  satisfactorily  determined  hj  the  investigations  of 
Melloni,  Laprovostaye,  and  Desains,  and  that  these  physicists 
have  practically  ascertained  the  reflective  power  of  polished 
silver  and  other  metals.  He  states,  also,  that  Laprovostaye 
and  Desains  have  shown  that,  "contrary  to  wliat  was  pre- 
viously supposed,  the  reflecting  power  varies  according  to  the 
source  of  heat."  "Thus,"  he  adds,  "the  reflecting  power  of 
polished  silver,  which  is  0.97  for  rays  from  a  Locatelli  lamp, 
is  only  0.92  for  solar  rays."  It  follows  from  this  announce- 
ment that  while  the  loss  of  radiant  energy  is  only  1.00  — 
0.97  =  0.03  Avhen  the  rays  emanate  from  the  lamp  mentioned, 
it  is  1.00  —  0.92  =  0.08  when  the  rays  from  the  sun  are 
reflected,  xiccordingly,  the  loss  of  energy  attending  reflec- 
tion will  be  nearly  three  times  greater  for  solar  heat  than 
for  artificial  heat.  That  such  a  difference  does  not  exist  is 
known  to  all  persons  conversant  with  reflectors.     Besides,  a 


CHAP.  MX.     BEFLECTIVi:  rOWEi:  OF  rOLlHUED  METALS.  295 

momeut's  consideration  of  the  properties  of  calorific  rays  suf- 
fices to  show  the  untenable  character  of  the  proposition, 
compelling  us  to  reject  Laprovostaye's  and  Desains's  investi- 
gation as  unrt'lial>le,  although  generally  accepted  by  plij- 
sicists.  Moreover,  the  table  of  reflective  power  of  various 
metals  presented  by  Deschanel  as  the  result  of  the  celebrated 
investigation  furnishes  additional  evidence  of  its  unreliable 
character.  Let  us  select  from  Laprovostaye  and  Desains's 
tabular  statement  the  relative  reflecting  capacity  of  silver 
and  brass.  The  former  is  represented  to  be  0.97,  while  the 
latter  is  0.93 ;  consequently,  the  reflective  powers  of  silver 
aii<l    brass    are   supposed    to    be    in    the    ratio  of    1.000  :  978, 

22 
difference  =  —--—'       Manufacturei's    of   reflectors    practicallv 
1000  ^  •' 

acquainted  with  the  subject  are  aware  that  silver  possesses 
a  far  greater  reflective  power  compared  with  brass  than  that 
indicated  by  the  stated  proportion. 

The  leading  feature  of  my  solar  engine  being  that  of 
developing  mechanical  power  by  concentrating  the  sun's 
radiant  heat,  the  efficacy  of  various  metals  for  this  purpose 
engaged  my  attention  during  the  early  stages  of  my  labora 
connected  with  utilizing  solar  energy  for  the  production  of 
motive  power.  Taking  for  granted  the  correctness  of  Lapro- 
vostaye's and  Desains's  statement  of  relative  efficacy,  I  con- 
structed reflectoi-s  composed  solely  of  brass,  in  oi-der  to  avoid 
the  great  cost  of  silver-plating.     The  difference  of  reflecting 

22 
power   asrreeablv  to    the    researches   referred   to    beincr  


•Zd6  BADIAXT  HEAT.  chap.  xix. 

ill   favor  of  silver,  I   simply   enlarged   the   reflectors    iii    that 

proportion,    expecting    to    produce    the    same    result    as    with 

22 

silver-i>lated     metals    preseutins;    less    area.      It   proved, 

^  ^  °    1000  ^  ' 

however,  im  the  tirst  trial,  that  the  reflective  capability  of 
Ijrass  is  far  inferior,  and  that  the  required  temperature 
could  not  be  produced  by  brass  I'eflectors ;  the  machine,  con- 
sequently, failing  to  operate  as  designed.  A  thorough  in- 
vestigation capable  of  determining  the  true  reflective  power 
of  various  metals,  therefore,  became  necessary;  but  before 
commencing  experiments,  the  method  resorted  to  by  Melloni, 
Laprovostaye,  and  Desains,  referred  to  by  Deschanel,  Avas 
carefully  examined.  The  said  method  is  thus  described  in 
his  "  Elementary  Treatise  on  Natural  Philosophy  "  :  "  The 
substance  under  investigation  is  placed  upon  a  circular  plate, 
Avliich  is  graduated  round  the  circumference.  The  thermo- 
electric pile  is  carried  by  a  horizontal  bar  which  turns  about 
a  pillar  supporting  the  circular  plate.  This  bar  is  so  ad- 
justed as  to  make  the  reflected  rays  impinge  upon  the  pile, 
the  adjustment  being  made  by  the  help  of  the  divisions 
marked  on  the  circular  plate.  In  making  an  observation, 
the  bar  is  iirst  placed  so  as  to  coincide  with  the  prolonga- 
tion of  the  said  principal  bar,  and  the  intensity  of  direct 
radiation  is  thus  observed.  The  pile  is  then  placed  so  as 
to  receive  the  reflected  rays,  and  the  ratio  of  intensity  thus 
obtained  to  the  intensity  of  direct  radiation  is  the  measure 
of  the  reflecting  power."  The  accompanying  sketch,  Fig.  3, 
represents  a  top  view  of  the  arrangement  referred  to  in  the 


CHAP.  XIX.     DEFLECTIVE  POWEE  OF  POLISHED  METALS. 


297 


above  explanation.  a  represents  a  Locatelli  lamp,  />  the 
graduatetl  circular  plate  on  wliicb  is  placed  the  polislied 
reflecting  substance  b',  and  c  the  tbermo-electrie  pile,  d 
shows  a  cluster  of  parallel  calorific  ra3's  projected  from  the 
lamp,  through  a  perforation  in  the  .screen  f,  toward.-;  the 
polished  substance  b'.  The  face  of  this  polished  substance 
being  jdaced  at  an  angle  of  45  deg.  to  the  course  of  the 
cluster  of  rays  d,  it  will  he  evident  that  the  I'ays  will  be 
deflected    at    the    same  angle ;   hence    the  cluster  will   be  di- 


rected as  shown  by  h,  ultimately  striking  the  face  of  the 
jiile  e.  The  latter,  it  should  be  mentioned,  is  protected 
against  radiation  from  the  lamp  by  a  screen  g.  The  tempe- 
rature imparted  by  the  deflected  radiant  heat  having  been 
recorded,  the  pile  is  allowed  to  cool,  and  then  placed  in  the 
position  c',  after  which  the  polished  substance  //  is  removed. 
As  the  radiant  heat  transmitted  by  the  parallel  rays  d  ema- 
nating from  the  lamp  will  now  act  directly  on  the  face  of 
the  pile,  a  higher  temperature  will  obviously  be  produced 
than  when  the  pile  occupied  the  position  c.     The  difference 


298  BADIANT  HEAT.  chap.  xix. 

of  temperature  thus  produced,  Ave  are  told,  indicates  exactly 
the  amount  of  loss  of  radiant  intensity  attending  the  reflec- 
tion of  the  rays  by  the  polished  substance  b'.  Laprovostaye 
and  Desains,  as  before  stated,  foimd  that  the  heat  trans- 
mitted directly  is  to  that  reflected  as  1.000  to  0.0V8,  hence 
the  loss  of  energy  =  0.022.  The  assumption  of  such  perfect 
reflective  poAver  being  palpably  erroneous,  let  us  examine 
carefully  the  adopted  method  in  order  to  detect  the  cause  of 
the  false  deduction.  Fig.  4  represents  a  top  view  of  Lapro- 
vostaye and  Desains's  arrangement,  already  described,  but 
drawn  to  a  larger  scale  than  in  Fig.  3,  similar  letters  of 
reference  being  employed  in  both  figures,  d  d  represents 
the  cluster  of  calorific  rays  transmitted  by  the  lamp  to  the 
polished  substance  V,  and  by  it  reflected,  as  shown  by  li,. 
towards  the  face  of  the  pile  c.  It  will  be  evident  that  the 
section  of  the  reflected  central  cluster  of  calorific  rays  de- 
pends upon,  and  corresponds  with,  the  face  of  the  pile  c, 
provided  the  perforation  in  the  screen  /  be  sufiiciently  large. 
It  will  also  be  evident  that  the  annular  cluster  Te  ^,  the 
external  diameter  of  which  depends  on  the  size  of  the  per- 
foration of  the  screen  /,  will  be  projected  towards  the 
polished  substance  I'.  Owing  to  defraction,  the  stated  an- 
nular cluster  will  expand  to  the  size  I  I  before  reaching  the 
substance  h',  and  thus  the  rays  become  dispersed  over  a 
considerable  portion  of  the  angular  face  of  b'.  Consequently, 
the  latter  will  become  heated,  and,  since  calorific  rays  radi- 
ate in  all  directions,  a  certain  amount  of  heat  will  be  trans- 
mitted to  the  pile  wholly  independent  of  that  propagated  by 


CHAP.  XIX.     DEFLECTIVE  roWEB  OF  POLTSFTED  METALS.  200 

the  defected  central  cluster  of  rays  represented  by  //.  But, 
after  taking  away  the  polished  substance  b',  and  moving  the 
pile  to  the  position  c'  (shown  in  Fig.  3),  the  pile  will  obvi- 
ously receive  heat  only  from  the  central  cluster  d  d.  AVe 
have  thus  demonstrated  that  more  heat  will  be  imparted  to 
the  pile  when  placed  in  the  position  c  than  when  placed  at 
c'  in  line  with  the  cluster  of  rays  d  d,  since  in  the  latter  case 
the  calorific  energy  due  to  the  section  of  rays  corresponding 
with  the  area  of  the  face  of  the  pile  can  alone  be  transmitted 
to  the  same.  Apart  from  this  cause  of  error,  it  should  be 
observed  that,  assuming  the  distance  a  b',  Fig.  3,  to  be  three 
times  greater  than  b'  c',  the  diverging  radiation  from  the 
heated  metal  of  the  lamp  will  subject  the  substance  b'  to  a 
greater  increase  of  temperature  than  that  to  which  the  pile 
is  subjected  when  at  c',  in  tlie  ratio  of  4'  to  3'.  The  effect  of 
this  in  causing  undue  transmission  of  heat  to  the  pile,  Avhen 
placed  at  c,  needs  no  explanation.  Several  other  causes  of 
error  inseparable  from  Laprovostaye  and  Desains's  method 
of  determining  the  reflective  power  of  metals  might  be 
sho^^-n.  Among  these,  the  inaccuracy  resulting  from  the  un- 
certain power  of  the  lamp  in  developing  a  uniform  amount 
of  heat  during  the  experiments  may  be  mentioned.  In 
view  of  the  foregoing,  it  is  evident  that  the  thermo-elec- 
tric method  is  unfit  to  determine  accurately  the  reflective 
power  of  different  substances.  And  it  may  be  demonstrated 
that,  unless  the  various  substances  under  examination  be 
exposed  simultaneously  to  a  common  source  of  heat,  the  rela- 
tive power  of  reflecting  calorific  raj-s  possessed  by  the  same 


300  BADIANT  BEAT.  chap.  xix. 

cannot  te  ascertained  witli  perfect  accuracy  by  any  method 
whatever.  The  instrument  illustrated  on  PL  30  has  been 
constructed  in  accordance  with  the  condition  thus  presented, 
the  source  of  heat  emjjloyed  being  solar  radiation.  The  fol- 
lowing somewhat  elaborate  description  and  explanation  have 
been  deemed  necessary  to  point  out  clearly  its  peculiar  fea- 
tures. Fig.  1  represents  a  vertical  section  of  the  instrument 
and  the  table  to  which  it  is  attached,  the  latter  being  pro- 
vided with  parallactic  mechanism  by  means  of  which  its 
face  is  kept  at  right  angles  to  the  sun  during  investiga- 
tions. Fig.  2  shows  a  top  view  of  the  instrument  as  seen 
from  a  point  situated  in  the  prolongation  of  its  axis,  at 
right  angles  to  the  face  of  the  table.  «  a  is  a  conical  re- 
flector composed  of  cast  iron,  the  sides  of  which  are  accu- 
rately turned  to  an  angle  of  45°  to  its  axis,  a  flat  bottom 
being  attached  provided  with  a  central  hub.  An  axle  h  is 
firmly  keyed  in  the  said  hub,  extending  both  above  and  be- 
low the  same.  The  lower  part  of  the  axle  turns  in  a  boss 
formed  on  opposite  sides  of  a  cross-piece  c  c,  the  latter  being 
supported  by  two  columns  bolted  to  the  parallactic  table. 
A  hand-wheel  d,  secured  to  the  axle  b,  enables  the  operator 
to  turn  the  conical  reflector  during  experiments.  Four  seg- 
mental heaters  /,  g,  Ji,  and  k,  precisely  alike,  composed  of  thin 
sheet  metal,  are  secured  to  the  bottom  of  the  reflector,  at 
equal  distance  from  the  centre,  with  intervening  spaces,  as 
shown  in  the  drawing ;  these  spaces  to  be  filled  with  some 
non-conducting  substance.  Each  heater  is  provided  with  a 
conical  socket  on  the  top,  into  which  a  perforated  cork  is  in-' 


CHAP.  XIX.     BEFLECTIYE  POWER  OF  POLISHED  METALS.  301 

serted  for  the  purpose  of  supporting  thermometei-s  entering 
the  fluid,  as  shown  in  the  sectional  representation.  It  is  im- 
portant to  observe  that,  before  being  attached  to  tlie  reflector, 
(^ach  heater  should  be  fille<l  with  water  of  a  given  tempera- 
ture and  accurately  \veighed.  In  case  of  any  difference  of 
weight,  small  quantities  of  soft  solder  should  be  gradually 
applied,  until  the  deficient  weight  is  made  good  and  the 
four  charged  heatera  balance  each  other  exactly.  Regarding 
the  construction  of  the  reflector  represented  by  the  illus- 
tration, it  remains  to  be  stated  that  four  segmental  plates 
f,  </',  7i',  and  k',  composed  respectively  of  silver,  brass,  nickel, 
and  steel,  precisely  alihe  in  size  and  form,  should  be  sol- 
dered to  the  inside  of  the  cone  n  n.  The  plates  being 
thus  secured  to  the  conical  surface,  the  reflector  should  be 
put  before  a  rotating  polishing  machine,  for  the  purpose  of 
having  an  equal  polish  imparted  to  each  plate. 

Referring  to  Fig.  2,  jt  will  be  seen  that  the  polished  seg- 
mental plates,  the  reflective  power  of  which  it  is  intended 
to  measure,  are  attached  opposite  to  the  heaters.  Thus  the 
plate  f,  composed  of  silver,  is  placed  exactly  opposite  to 
the  heater  //  the  brass  plate  g'  opposite  to  the  heater  g ; 
the  remaining  plates  h'  and  Tc',  composed  respectively  of 
nickel  and  steel,  being  likewise  placed  opposite  to  their  cor- 
responding heatei*s  h  and  h. 

Referring  to  the  vertical  section  of  the  instrument  shown 
in  Fig.  1,  supposed  to  be  turned  towards  the  sun,  it  will  be 
seen  that  the  solar  rays  m,  n,  indicated  hy  dotted  lines,  are 
reflected  by  the  polished  segmental  plates  towards  the  semi- 


30a  RADIANT  HEAT.  chap.  xix. 

circular  faces  of  the  heaters.  The  areas  of  the  polished 
plates  being  alike,  while  the  Aveight  aud  areas  of  the  lieat- 
ers  presented  to  the  reflected  solar  heat  are  also  alike,  it 
follows  that  if  the  reflective  power  of  the  several  plates 
does  not  vary,  the  thermometers  inserted  in  the  heaters  will 
show  an  equal  increase  of  temperature  during  equal  inter- 
vals of  time.  But  should  the  segmental  plates  not  possess 
an  equal  power  of  reflecting  the  energy  transmitted  by  the 
solar  rays,  the  thermometers  will,  after  a  brief  exposure  to 
the  sun,  indicate  different  temperatures.  Obviously  the  dif- 
ferential temperature  reached  by  each  thermometer  in  the 
same  time  will  furnish  a  true  indication  of  the  relative  re- 
flective power  of  the  sevei'al  segmental  plates,  j)rovided 
there  are  no  disturbing  causes  affecting  the  heaters  un- 
equally. Before  examining  this  important  point,  it  will  be 
proper  to  observe  that  the  internal  diameter  of  the  conical 
reflector  at  n  ii  is  2.5  times  greater  than  the  external  dia- 
meter of  the  heaters  at  o  o;  hence  the  radiant  intensity 
transmitted  to  their  faces  will  be  2.5  times  greater  than 
the  direct  radiant  intensity  conveyed  by  the  rays  m  n.  It 
shoiild  be  particularly  observed  that  while  the  effect  of  this 
concentration  of  heat  will  influence  the  four  heaters  alike, 
it  greatly  increases  the  sensitiveness  of  the  instrument,  since 
the  thermometers  "will  be  siibjected  to  a  radiant  energy  2.5 
greater  than  that  produced  by  the  direct  action  of  the  sun's 
rays,  less  the  loss  occasioned  by  the  imperfect  reflective 
power  of  the  segmental  plates,  together  with  the  losses  of 
heat    caused    by  convection  and  radiation.      It  will  be  seen, 


CHAP.  XIX.    BEFLECTIYE  POWER  OF  POLISHED  METALS.  303 

on  inspecting  the  vertical  section  in  Fig.  1,  tliat  the  lowei' 
heater  will  be  subjected  to  the  cooling  influence  of  the  up- 
ward current  of  the  air  caused  by  the  heat  imparted  by 
contact  with  the  lower  side  of  the  heater.  The  upper 
heater,  on  the  other  hand,  ^\•ill  not  be  subjected  to  any  ap- 
preciable loss  of  heat  by  convection,  other  than  that  which 
is  shared  by  the  lower  heater.  It  is  hardly  necessary  to 
point  out  that  the  conical  reflector  itself  cannot  be  main- 
tained at  a  uniform  temperature  all  over,  owing  to  the  pow- 
erful upAvard  current  of  air  unavoidable  in  a  place  exposed 
to  the  sun's  rays.  The  apparently  insuperable  difiiculties 
thus  presented,  and  nuuij^  others  of  minor  importance,  are 
overcome  by  the  simple  expedient  of  causing  the  reflector  to 
revolve  during  the  investigation.  The  rotary  motion  is  ef- 
fected, as  already  stated,  by  means  of  the  hand-wheel  d, 
\\\\'\c\i  is  kept  revolving  at  the  rate  of  about  six  turns  per 
minute  while  the  heaters  are  being  exposed  to  the  reflected 
and  concentrated  solar  heat.  It  needs  no  demonstration  to 
prove  that  by  this  expedient  all  disturbing  influences  will 
affect  the  four  heaters  alihe,  thereby  neutralizing  the  same 
as  completely  as  if  no  disturbance  existed.  The  nature  of 
the  device  having  been  thus  minutely  described,  let  us 
now  consider  the  mode  of  managing  the  same  during  the 
investigation.  (1)  Before  turning  the  reflector  towards  the 
sun,   bring    the    parallactic    table   to    a   horizontal    position. 

(2)  Remove  the  corks  and  thermometers,  and  fill  the  heat- 
ers with  water  of  the  same  temperature  as  the   atmosphere. 

(3)  Keplace    the    corks    and    thermometers,    and    bring    the 


301  ItABIAyT  MEAT.  chap.  xix. 

table  to  an  inclined  position  corresponding  with  the  sun's 
zenith  distance.  (4)  In  order  to  ensure  a  perfect  mixture 
of  the  particles  of  water  in  the  heaters,  turn  the  reflector 
for  about  two  minutes.  (5)  The  rotation  being  then  stop- 
ped, note  carefully  the  indication  of  the  thermometers,  and 
keep  a  separate  record  for  each  heater  and  corresponding 
segmental  plate.  (6)  The  initial  temperatures  having  been 
thus  ascertained,  and  the  parallactic  table  and  reflector 
turned  to  the  sun,  the  hand-wheel  should  be  kept  in  con- 
tinuous motion,  at  the  I'ate  before  mentioned,  for  a  period 
of  ten  minutes.  (7)  At  the  expii-ation  of  the  stated  time 
the  motion  to  be  suflficiently  reduced  to  admit  of  reading 
the  thermometers,  two  observers  being  emplo}ed  for  that 
purpose.  If  the  investigation  be  conducted  at  noon,  dniing 
the  winter  season — the  most  favorable  for  accurate  observa- 
tion— it  will  be  well  to  continue  the  experiment  for  fifty 
minutes,  the  indications  of  the  thermometers  being  noted  at 
the  termination  of  eveiy  other  minute,  after  the  expiration 
of  the  fii'st  ten  minutes  before  adverted  to.  It  might  be  sup- 
posed that  an  observation  at  the  expiration  of  the  10th  and 
50th  minutes  Avould  suflice  to  ascertain  the  dift'ereutial  tem- 
perature imparted  by  the  reflected  and  concentrated  rays  to 
each  heater;  and  that  by  the  observed  difference  of  indica- 
tion the  comparative  reflective  power  of  the  several  seg- 
mental plates  might  be  accurately  determined.  But  it  will 
be  perceived,  on  due  consideration,  that  in  case  of  defects, 
such  as  imperceptible  leaks  or  impei'fect  circulation,  the  re- 
corded  temperature   would  lead  to  a  false  determination  of 


CHAP.  XIX.     EEFLECTIVE  rOWEli  OF  FOLiaUED  METALS.  305 

the  comparative  reflective  properties.  Numerous  observa- 
tions at  definite  intervals  during  tlie  experiment  will  evi- 
dently serve  as  effectual  checks.  Of  course,  if  equal  reflective 
power  of  the  respective  plates  results  from  each  of  these 
observations,  then  the  accuracy  of  the  determination  may  be 
regarded  as  absolutely  certain.  Regarding  the  initial  tempe- 
rature of  the  heatei-s,  it  will  be  perceived  that  if  at  starting 
the  indications  of  all  the  thermometers  corresponded,  the 
comparison  of  the  reflective  power  of  the  plates  would  be 
very  simple ;  but  experience  has  shown  that  a  perfectly  equal 
temperature  at  starting  is  impracticable.  Consequently,  each 
plate,  with  its  corresponding  heater  and  thermometer,  calls 
for  a  separate  record. 

It  is  worthy  of  notice  that  investigations  intended  to  deter- 
mine the  dynamic  energy  of  solar  radiation  are  rendered  very 
diflioult,  because  the  heat  acts  on  the  upper  part  of  any  fluid 
intended  to  absorb  it.  Artificial  means  must  therefore  be 
employed  to  cause  circulation,  or  mixture,  of  the  particles 
within  the  mass  exposed  to  the  solar  rays.  The  difficulty 
attending  artificial  circulation,  and  the  complicated  character 
of  the  means  necessary  to  promote  a  thorough  mixture  of 
particles  when  a  fluid  is  heated  from  above,  has  been  shown 
in  Chapter  V.  Nor  can  it  be  denied  that,  notwithstanding 
the  elaborate  character  of  those  means,  the  object  has  been 
but  partially  attained.  In  the  present  instance,  however, 
the  circulation  or  mixture  of  heated  and  colder  particles  of 
the  fluid  within  the  heaters  is  absolutely  perfect ;  since,  for 
each  revolution  of  the  reflector,  the  colder  particles  are  trans- 


306  RADIANT  HEAT.  CHAP.  XIX. 

ferred  from  the   buttuiu  to  the  top  of  the   vessel,   tmd   vice 
versd. 

Before  presenting  the  result  of  our  iuvestigatiou  of  the 
comparative  reflective  power  of  silver  aud  othei'  metals,  it 
will  be  necessary  to  explain  the  nature  of  the  annexed  tables. 
We  have  just  stated  that,  owing  to  the  impossibility  of  ensur- 
ing a  uniform  initial  temperature,  each  of  the  four  polished 
plates  attached  to  the  inside  of  the  conical  reflector  has  called 
for  a  separate  record.  The  tables,  accordingly,  contain  four 
distinct  divisions,  headed  respectively  silver,  hra^is:,  niclcel,  and 
steel ;  each  division  having  a  different  initial  temperature,  viz., 
silver,  G5°.7  ;  brass,  66°. 1 ;  nickel,  65°. 4  ;  and  steel,  6.j°.l  F.  As 
the  temperatures  recorded  in  the  table  commence  at  the  ter- 
mination of  the  toitli  minute  from  starting,  the  oi-iginal  initial 
temperatures  have  not  been  entered,  excepting  that  of  the 
heater  exposed  to  the  solar  rays  reflected  by  the  silver  plate, 
Avhicli  forms  the  standard  of  comparison.  The  headings  of 
the  several  columns  of  the  tables  being  sufficiently  explana- 
tory, it  will  only  be  necessary  to  point  out  the  mode  of  deter- 
mining the  relative  reflective  power  of  the  segmental  plates. 
Let  us  select  the  nickel  plate.  Eeferring  to  the  table,  it  will 
be  found  that,  at  the  termination  of  the  30th  minute  from 
starting,  the  thermometer  inserted  in  the  heater  li  indicated 
89°.5,  while  the  initial  temperature  in  that  heater  was  65°.4 ; 
hence  an  increase  of  89.5  —  65.4  =  24°.l  during  30  minutes. 
During  the  same  period  the  temperature  of  the  heater  /,  sub- 
jected to  the  reflected  solar  rays  from  the  silver  plate  /'',  it 
will  be  seen,  by  referring  to  the  table,  increased  96.4  —  65.7 


CH  vi'.  XIX.     liEFLECriVE  I'OWEU  OF  POLISHED  METALS. 


307 


I'able  siiowino  Tin 

liKLATIVi 

Reflective  Powei 

OF 

Polished  Metals. 

a 

SILVES. 

SRASS. 

-si 

If 

■si 

11 
5| 

li 

3| 

ll 

O  H 

IB 

£    '5 

■gas 

•7i 

Jftn. 

'  F^ih. 

'Fah. 

°I-ah. 

'Fah. 

'Fall. 

Ratio. 

10 

78.8 

13.1 

65.7 

77.4 

11.6 

0.885 

12 

80.9 

15.2 

65.7 

79.6 

13.4 

0.881 

14 

83.1 

17.4 

65.7 

81.5 

15.4 

0.885 

16 

8o.0 

19.3 

65.7 

83.2 

17.1 

0.885 

IS 

87.1 

21.4 

65.7 

85.1 

19.0 

0.887 

20 

88.6 

22.9 

65.7 

86.4 

20.3 

0.886 

22 

90.2 

24.5 

65.7 

87.7 

21.6 

0.881 

24 

91.6 

25.9 

65.7 

89.2 

23.1 

0.891 

26 

93.3 

27.6 

65.7 

90.8 

23.7 

0.858 

28 

94.9 

29.2 

65.7 

92.2 

26.1 

0.894 

30 

96.4 

30.7 

65.7 

93.5 

27.4 

0.892 

32 

97.6 

31.9 

65.7 

94.3 

28.2 

0.884 

34 

98.4 

32.7 

65.7 

95.4 

29.3 

0.896 

36 

99.7 

34.0 

65.7 

96.5 

30.4 

0.894 

38 

100.8 

35.1 

65.7 

97.3 

31.2 

0.888 

40 

102.0 

36.3 

65.7 

98.4 

32.3 

0.889 

42 

103.4 

37.7 

65.7 

99.5 

33.4 

0.886 

44 

104.0 

38.3 

65.7 

100.0 

33.9 

0.885 

46 

104.7 

30.0 

65.7 

100.5 

34.4 

0.882 

48 

105.3 

39.6 

65.7     1 

100.9 

34.8 

0.878 

50 

105.9 

40.2 

65.7     1 

101.4 

35.3 
Mean 

0.878 

=  0.885 

308 


RADIANT  HEAT. 


CHAP.  XIX. 


Table  showing  the  Relative  Eeflective  Power  of 

Polished  Metals. 

H 

NICKEL. 

STEEL. 

la 

c  1 

Increase  of 
temperature. 
Initial,  C5°.4. 

£    '3 

|| 

c  a 

las" 

*5  c;  to 

Min. 

'  Fall. 

°Fah. 

Ratio. 

°  Fah. 

°  Fah. 

Ratio. 

10 

75.5 

10.1 

0.771 

74.1 

9.0 

0.687 

12 

77.2 

11.8 

0.776 

75.6 

10.5 

0.684 

14 

78.8 

13.4 

0.770 

77.0 

11.9 

0.683 

16 

80.3 

14.9 

0.772 

78.4 

13.3 

0.689 

18 

82.0 

16.6 

0.776 

79.9 

14.8 

0.691 

20 

83.2 

17.8 

0.777 

81.1 

16.0 

0.699 

22 

84.5 

19.1 

0.779 

82.3 

17.2 

0.702 

24 

85.7 

20.3 

0.783 

83.4 

18.3 

0.706 

26 

8G.7 

21.3 

0.772 

84.2 

19.1 

0.692 

28 

87.6 

22.2 

0.760 

85.9 

20.8 

0.712 

30 

89.5 

24.1 

0.785 

87.1 

22.0 

0.716 

32 

90.4 

25.0 

0.783 

87.7 

22.6 

0.708 

34 

91.4 

26.0 

0.795 

88.5 

23.4 

0.715 

36 

92.3 

26.9 

0.791 

89.5 

24.4 

0.717 

38 

93.2 

27.8 

0.792 

90.1 

25.0 

0.712 

40 

94.2 

28.8 

0.793 

91.0 

25.9 

0.713 

42 

95.3 

29.9 

0.799 

91.8 

26.7 

0.708 

44 

95.7 

30.3 

0.791 

92.5 

27.4 

0.715 

46 

96.1 

30.7 

0.787 

92.8 

27.7 

0.710 

48 

97.0 

31.6 

0.797 

93.3 

28.2 

0.712 

50 

97.5 

32.1 
Mean  = 

0.798 

94.0 

28.9 
Mean 

0.718 

=  0.786 

=  0.709 

CHAP.  XIX.     EEFLECTIVE  I'OWEE  OF  POLISHEB  METALS.  309 

=  iJO.T.  Consequently,  the  reflective  power  of  silver  is  to 
that  of  nickel  as  30°.7  to  24M  =  1.000  to  0.785.  Now,  it 
will  be  fmiiul,  on  inspecting  the  table,  that  the  reflective 
power  of  nickel,  determined  by  the  mean  of  twenty-five  dis- 
tinct observations,  is  0.786  against  the  stated  0.785.  This 
insignificant  difference  furnishes  positive  evidence  of  the  reli- 
able character  of  the  investigation.  The  important  question 
of  comparative  reflective  power  of  silver,  brass,  nickel,  and 
steel  may  therefore  be  regarded  as  permanently  settled  ;  while 
the  reflective  power  of  all  other  metals  may  be  determined 
in  like  maniici-,  by  simply  detaching  the  brass,  nickel,  and 
steel  plates  from  the  conical  reflector  and  substituting  others 
in  their  places ;  the  silver  plate,  of  couree,  remaining  as  a 
standard  of  comijarison.  It  has  already  been  stated  that, 
according  to  Laprovostaye  and  Desains's  investigation,  the 
reflective  power  of  brass  is  to  that  of  silver  Jis  0.978  to 
1.000,  difference  =  0.022,  while  our  exact  method  of  measur- 
ing the  energy  lost  by  reflection  shows  that  brass  possesses 

885 

a  reflecting  power  of  only  of  that  of  silver,  difference 

°  '■  •'    1000 

1.000  —  0.885  =  0.115  against  0.022.  Considering  the  precision 
which  distinguishes  all  Laprovostaye  and  Desains's  investi- 
gations, this  extraordinary  discrepancy  proves  indisputably 
that  the  exact  loss  of  calorific  energy  attending  the  reflection 
of  radiant  heat  cannot  be  ascertained  by  the  thermo-electric 
method. 


CHAPTER   XX. 


RAPID-INDICATION  ACTINOMETER. 


Physical  observatories  cannot  be  regarded  as  fully  equip- 
ped unless  provided  with  actiiiometers  })y  means  of  wliieli 
the  intensity  of  solar  radiation  may  be  quickly  ascertained, 
say  in  the  course  of  one  minute.  The  thermo-electric  pile 
is  of  no  avail  for  this  pur^iose,  from  varioiis  reasons:  (1) 
The  temperature  produced  by  solar  radiation  is  too  high  to 
be  correctly  registered  by  the  deflection  of  the  galvanometric 
needle ;  (2)  The  degree  of  actual  temperature  inferred  from 
the  ai'c  described  by  the  needle  is  mere  guess-work  at  the 
high  temperature  developed  by  a  vertical  sun ;  (3)  The 
disturl)ing  effects  of  movable  masses  of  iron,  the  jiresence  of 
^vhich  are  unavoidable;  (4)  The  rotation  of  the  obsei-vatory 
and  consequent  irregular  change  of  the  magnetic  meridian. 

The  illustration  on  PI.  31  represents  a  vertical  section  of 
an  instrument  constructed  for  the  special  purpose  of  ascer- 
taining the  intensity  of  the  radiant  heat  after  a  very  brief 
exposure  to  the  sun's  rays.     The  leading  feature  of  the  de- 


cu.U>.  XX.  UAriD-lSUlCATWy  ACTlSOMElEli.  311 

viit'  is  iliat  of  coueeutratiiig  the  rays  before  reaching  the 
bull)  ut'  tlie  thermometer  employed  to  measure  the  iuteusity. 
It  will  be  leadily  understood  that  by  employing  a  lens  of 
[H'opiT  t'nrm  the  degree  of  concentration  may  be  such  that 
in  the  space  of  sixty  seconds  the  mercurial  column  of  the 
thermometer  subjected  to  the  concentrated  I'ays  will  rise  to 
the  same  height  as  the  column  of  another  thermometer  ex- 
posed to  the  direct  influence  of  the  sun's  radiant  luat  (hiring 
a  period  sufficient  to  produce  maximum  indication.  Hence, 
assuming  that  a  proper  degree  of  concentration  has  been  at- 
tained ill  the  iifw  iustnimeiit,  its  exposure  to  the  suii  during 
sixty  seconds  will  obviously  funiisli  an  indication  of  the 
intensity  of  the  sun's  rays  as  C(jrrectly  as  the  actinometer 
described  in  Chap.  III.,  whatever  be  the  zenith  distance  or 
other  conditions  at  the  time  of  making  the  observation.  The 
concentration  of  the  sun's  rays,  it  should  be  observed,  nuist 
take  place  within  an  exhausted  vessel  maintained  at  a  con- 
stant temperature  corresponding  with  that  of  the  actinometer 
referred  to.  It  is  hardly  net'cssaiy  to  point  out  that  it 
would  be  impossible  to  determine  theoretically  the  precise 
distance  between  the  lens  employed  to  concentrate  the  rays 
and  the  thermometer  ^\hich  receives  the  accumulated  heat. 
The  instrument  should  therefore  be  so  constructed  that  the 
lens  may  be  readily  moved  away  from  or  towards  the 
thermometer  during  observations.  This  property  of  the  in- 
strument under  consideration  may  be  regarded  as  another 
leading  feature  indispensable  to  render  accurate  adjustment 
practicable.      Referring   to    the    illustration,   it    will    be   seen 


312  BADIAM  HEA  T.  CHAP.  xx. 

tliat  tlie  exhausted  vessel  euclosing  the  recording  tLeniiometer 
is  surroiiuded  by  an  external  casing,  the  form  of  which,  like 
the  internal  vessel,  is  cylindrical.  The  intervening  space  is 
tilled  with  water  maintained  at  a  constant  temperature  by  a 
similar  process  of  circulation  as  that  adopted  in  the  actino- 
nieter  described  in  Chap.  III.  Couplings  for  attaching  the 
circulating  tubes  are  applied  at  the  bottom  and  top  of  the 
external  casing,  as  shown  in  the  illustration.  The  inclina- 
tion of  the  cylindrical  vessel  is  regulated  by  a  tangential 
screw  ^\'orking  through  a  nut  turning  in  bearings  attached  to 
the  side  of  the  external  vessel.  By  means  of  the  graduated 
quadrant  represented  in  the  illustration,  the  sun's  zenith 
distance  may  be  ascertained  by  mere  inspection,  at  all  times, 
during  observations.  A  journal  applied  under  the  exhausted 
vessel  coinciding  with  the  centre  of  the  graduated  quadrant, 
and  turning  in  appropriate  bearings,  suppoi"ts  the  instrument. 
These  bearings  are  secured  to  the  top  of  a  vertical  column 
resting  on  a  revolving  circular  plate,  to  which  a  small  pinion 
is  applied,  as  shown  in  the  illustration.  This  j)inion,  intended 
to  be  operated  by  hand,  works  into  cogs  formed  at  the  cir- 
cumference of  the  circular  bed-plate  attached  to  the  top  of 
a  substantial  table.  The  tangential  screw,  it  will  be  seen, 
is  provided  with  a  small  hand-wheel  at  the  lower  end, 
enabling  the  operator  to  give  any  desired  inclination  to  the 
instrument,  while  the  small  hand-wheel  of  the  pinion,  before 
referred  to,  enables  him  to  follow  the  earth's  diurnal  motion. 
Let  us  now  examine  the  mode  of  regulating  the  distance 
between  the  lens  and  the  thermometer  which  is  employed  to 


CHAP.  XX.  EAriD-IXDICATIOX  ACTIXOMETER.  313 

show  the  intensity  of  the  concentrated  radiant  heat.  We 
have  already  pointed  out  that  it  is  impossible  to  determine 
theoretically  the  said  distance.  Of  course,  it  may  be  calcu- 
lated approximately,  but  not  sufficiently  near  to  dispense 
with  means  admitting  of  a  very  considerable  movement  of 
the  lens  up  and  down  during  the  process  of  adjustment.  In 
order  to  meet  this  condition,  the  lens  is  inserted  in  a  per- 
forated piston  fitting  air-tight  in  the  exhausted  cylindrical 
vessel ;  the  latter  being  bored  out  accurately  like  the  barrel 
of  an  air-pump.  The  adjustment  of  the  position  of  the  lens, 
it  will  be  seen  by  referring  to  the  illustration,  is  effected  by 
screws  secured  in  the  piston,  the  nuts  employed  for  raising 
the  same  acting  against  substantial  brackets  bolted  to  the 
top  riange  at  the  upper  end  of  the  exhausted  cylinder.  Con- 
venient means  being  thus  arranged  for  raising  or  lowering 
the  lens  in  the  exhausted  cylinder,  it  will  be  perceived  on 
reflection  that  although  the  thermometer  subjected  to  the 
action  of  the  concentrated  heat  is  graduated  in  the  ordinary 
manner,  its  indication  may  be  made  to  correspond  exactly 
with  that  of  an  actinometer  exposed  to  the  direct  action  of 
the  sun's  rays,  provided  the  piston  be  placed  correctly,  viz., 
at  such  a  distance  that  the  energy  of  the  convei'ged  rays 
under  the  lens  be  sufficient  to  raise  the  mercurial  column  of 
the  enclosed  thermometer  as  high  during  an  interval  of  sixty 
seconds  as  that  of  an  actinometer  exposed  to  the  direct  solar 
heat  during  a  period  sufficient  to  produce  maximum  indica- 
tion. It  will  lie  admitted  that  but  for  the  introduction  of 
a  movable  lens  it  would    be    impracticable    to    construct    an 


314  BABIANT  HEAT.  chap.  xx. 

instrument  furnishing  maximiim  indication  of  solar  intensity 
during  tlie  exact  interval  of  sixtij  seconds.  The  expedient, 
however,  of  inserting  the  lens  in  a  piston  capable  of  being 
l^laced  at  any  desirable  distance  in  order  to  subject  the  bulb 
of  the  enclosed  thermometer  to  any  requisite  temperature,  it 
Avill  be  perceived,  renders  that  adjustment  easy  which  is 
necessary  to  secui'e  a  given  indication  in  a  stipulated  time. 

It  has  been  pointed  out  in  previous  chapters  that,  owing 
to  the  rapid  change  of  zenith  distance,  and  the  consequent 
variation  of  the  depth  of  atmosphere  penetrated  by  the  sun's 
rays,  the  indication  of  an  actinometer  is  too  loAV  during  the 
forenoon  and  too  high  in  the  afternoon.  It  will  be  obvious, 
therefore,  that  the  lens-instrument  under  consideration  should 
be  adjusted  when  the  sun  passes  the  meridian,  since  the  acti- 
nometer employed  for  comparison  then  indicates  correctly  the 
solar  intensity  at  the  moment  of  making  the  observation. 
The  adjustment  is  effected  in  the  following  manner :  Having 
placed  the  lens-instrument  by  the  side  of  the  standard  acti- 
nometer selected  for  comparison,  the  casings  or  water-jackets 
of  the  two  should  be  connected,  by  means  of  flexible  tubes, 
in  such  a  manner  that  the  outlet  pipe  of  the  actinometer  is 
made  to  communicate  with  the  inlet  pipe  of  the  lens-instru- 
ment. Both  instruments  having  been  tui'ned  towards  the  sun, 
and  the  usual  connections  to  the  cistern  and  hand-pump  of  the 
actinometer  having  been  completed,  the  refrigerating  current 
should  be  circulated  through  the  jackets  until  the  actinometer 
indicates  maximum  differential  temperature.  In  the  mean- 
time, the  operator  attending  to  the  circulation  should  screen 


CHAP.  XX.  RAPID-INDICATION  ACTINOMEXmi.  315 

the  lens-iustrunient  from  tlie  sun  by  a  disc  of  pasteboard.  A 
second  operator,  as  soon  as  maximum  temperature  lias  been 
reached  by  the  actinometer,  starts  the  chronograph  and  calls 
time,  the  pasteboard  screen  being  at  once  lowered.  At  the 
termination  of  sixty  seconds,  time  is  again  called,  and  the 
protecting  screen  instantly  raised.  Let  us  now  suppose  that 
the  actinometer  has  continued  to  indicate  a  differential  tem- 
perature of  5G°  during  the  experiment,  and  that  the  thermo- 
meter of  the  lens-instrument  indicates  only  oS""  at  the  end 
of  sixty  seconds'  exposure  to  the  concentrated  solar  a-adiation. 
It  needs  no  explanation  to  show  that  the  observed  difference 
of  56  —  52  =  4°  is  owing  to  the  want  of  adequate  concen- 
tration, and  that  the  discrepancy  will  be  remedied  simply 
by  moving  the  lens  further  from  the  enclosed  thermometer. 
This  is  effected  by  turning  each  of  the  nuts  at  the  top  of 
the  exhausted  cylinder,  say  once  round,  thereby  increasing 
the  distance.  The  chronograph  should  again  be  started,  the 
screen  removed,  and  the  operation  already  described  repeated 
as  quickly  as  possible,  and  the  result  recorded.  Should  it 
now  be  found  that  the  enclosed  thermometer  indicates  54°, 
another  turn  of  the  adjusting  nuts  should  be  given,  and  the 
operation  repeated  a  third  time.  Due  diligence  being  exer- 
ci^^ed  by  the  operators,  the  proper  position  of  the  lens  may 
thus  be  determined  before  a  change  of  the  sun's  zenith  dis- 
tance takes  place  sufficient  to  affect  the  indication  of  the 
standard  actinometer  to  an  extent  preventing  accurate  adjust- 
ment. In  view  of  the  fact  that  the  form  of  the  lens,  and 
its  distance  from  the  thermometer  which  indicates  the  inten- 


316  BABIANT  HEAT.  chap.  xx. 

sity  of  the  concentrated  radiation,  may  be  approximately 
determined  by  calculation,  it  is  evident  that  tlie  lens  might 
be  stationary  and  the  recording  thermometer  graduated  by 
repeated  exposure  to  the  sun  during  intervals  of  60  seconds, 
so  as  to  correspond  with  the  indication  of  a  standard  actiuo- 
meter.  I  have  constructed  small  lens-actinometers  on  this 
plan,  useful  for  ordinary  observations,  but  for  physical  obser- 
vatories and  investigations  requiring  perfect  accuracy  the 
instrument  having  a  movable  lens,  as  represented  by  the 
illustration  in  PL  31,  is  far  preferable. 


CHAPTER  XXI. 


SOLAR  RADIATION   AND   DIATHERMANCY   OF   FLAMES. 


The  readers  of  "  Coiiiptes  Rendus "  are  a^vare  tLat  Pere 
Secchi  addressed  a  letter  to  the  Academy  of  Sciences  at 
Pans  (see  "Comp.  Rend.,"  tome  Ixxiv.,  pp.  26-30),  contain- 
ing a  review  of  my  communications  to  JVatvre,  publislied 
July  13,  October  5,  and  November  16,  1871,  in  wliicli  he 
questions  the  correctness  of  my  published  reports  containing 
tabulated  statements  of  the  temperatm-e  produced  by  solar 
radiation.  His  reason  for  questioning  the  reliability  of  my 
tables  appears  to  rest  on  the  supposition  that  my  instruments 
do  not  furnish  correct  indications.  "It  is  astonishing,"  he 
says,  "  that  Mr.  Ericsson  should  find  with  his  instrument  a 
higher  stationaiy  temperature  in  winter  than  in  summer. 
This  (even  bearing  in  mind  the  greater  proximity  of  the  sun 
in  winter)  makes  me  think  that  there  must  be  something 
very  singular  in  his  apparatiis,  making  all  its  indications 
deceptive.  Even  under  the  beautiful  sky  of  Madrid  has  M. 
Rico  y  Sinobas  found,  in  December,  for  the  solar  radiation, 
12    div.,    19  by   his  actinometer,  and,  in  June,   25   div.,   56." 


318  BADIANT  HEAT.  chap.  xxi. 

P^re  Secclii  ought  to  liave  2:)erceived  "tliat  there  must  be 
sometliiug  very  singular  "  in  the  actinometer  emj)loyed  by  the 
Spanish  physicist,  or  it  could  not  have  indicated  an  intensity 
twice  as  high  in  June  as  in  December.  Obviously,  a  correct 
actinometer  will  indicate  a  higher  temperature  during  the 
^vinter  solstice  than  at  midsummer  f<.)r  equal  zenith  distance. 
The  instrument  employed  at  Madrid,  if  Secchi's  figures  are 
correct,  must  therefore  be  founded  on  utterly  erroneous  prin- 
ciples. In  North  America,  in  lat.  40  deg.  42  min.  (the 
latitude  of  Madrid  is  40  deg.  24  min.),  solar  intensity  at  noon 
during  the  latter  part  of  June  is  64°. 5  when  the  shy  is 
clear,  while  at  noon  during  the  latter  part  of  December  the 
temperature  under  similar  atmospheric  conditions  reaches 
57°.70.  But  observations  made  in  the  morning  or  evening 
during  the  month  of  June,  at  the  hour  when  the  sun's  alti- 
tude is  the  same  as  at  noon  in  December,  show  that  the 
intensity  of  the  radiant  heat  in  June  is  only  53°. 08,  against 
57°.49  F.  in  December.  Actual  observations  have  thus 
established  the  fact  that  for  corresjyonding  zenith  disfauce  the 
temperature  produced  by  the  radiant  heat  Avhen  the  earth  has 
nearly  reached  perihelion,  is  57°.49  —  53°.0S  =  4°.41  higher 
than  at  midsummer.  Referring  to  Chap.  IV.,  it  Avill  be  seen 
that,  owing  to  the  greater  proximit}'  of  the  sun,  the  increase 
of  absolute  intensity  of  solar  radiation  is  4°.GG  F.  during  the 
winter  solstice.  Pere  Secchi  will  do  well  to  examine  the  sub- 
ject more  carefully,  and  make  himself  better  acquainted  with 
the  character  of  the  investigations  which  have  led  to  an  exact 
determination  of  the  temperature  produced  by  solar  radiation. 


CHAP.  xxi.        SOLAR  rADIATIOX  AXV  DIATnEEMANOT.  319 

The  readers  of  "  Comptes  Rendus  "  who  have  examined  the 
review  referred  to,  ignoraut  of  the  articles  in  Nature,  the 
contents  of  which  Pere  Secchi  criticises,  will  be  surprised  to 
learn  that  I  have  not,  as  the  revieAver  asserts,  questioned  the 
power  of  vapo)'  to  diminish  solar  intensity.  Having  stated 
the  result  of  numerous  observations  of  the  sun's  radiant  pow  er 
at  corresponding  zenith  distance,  and  proved  that  the  tempe- 
rature during  midwinter  is  higher  than  at  midsunuuer,  I  made 
the  following  remark  in  Kature,  Nov.  1(5,  1S71  :  "In  the  face 
of  such  facts  it  is  idle  to  contend  that  the  temperature  pro- 
duced by  solar  radiation  under  coiTesponding  zenith  distance 
and  a  clear  skij  varies  from  any  other  cause  than  the  vaiying 
distance  between  the  sun  and  the  eartli."  It  is  absurd  to 
suppose  that  a  person  having  devoted  many  years  to  the 
investigation  of  solar  radiation  should  deny  the  retarding 
influence  of  vapor,  since  not  one  observation  in  a  hundred 
indicates  maximum  solar  intensity,  owing  to  the  presence  of 
vapor  in  the  atmosphere. 

The  following  brief  description  of  the  actinometer  which 
Pere  Secchi  supposed  to  be  constructed  on  erroneous  prin- 
ciples was  inserted  in  my  reply  to  his  criticism  published  in 
"  Comptes  Rendus,"  before  referred  to,  in  hopes  that,  on  learn- 
ing that  there  is  not  anything  "very  singular"  in  my  appa- 
ratus, lie  would  have  seen  fit  to  witlidraw  Iiis  statement 
(piestioning  the  correctness  of  my  observations  relating  to 
solar  intensity :  "  The  principal  part  of  the  instrument  con- 
sists of  an  air-tight  cylindrical  vessel,  the  axis  of  which  is 
directed  towards  the  sun,  the  upper  end  l)eing  provided  with 


320  BADIANT  HEAT.  chap.  xxi. 

a  thin  lens  covering  an  aperture  3  ins.  in  diameter.  The 
bnllj  and  part  of  the  stem  of  a  mercurial  thermometer  is 
inserted  through  the  u^'per  side,  at  right  angles  to  the  axis, 
a  small  air-pump  being  applied  for  exhausting  the  air  fi-om 
the  cylindrical  vessel.  The  latter  is  surrounded  liy  a  casing 
through  which  water  is  circulated  by  means  of  an  ordinary 
force-pump  and  ilexible  tubes,  connected  with  a  capacious 
cistern  containing  water  kept  at  a  constant  temperature  of 
(50°  F.  The  bulb  of  the  thermometer  is  cylindi'ical,  3  ins. 
long,  its  contents  bearing  a  very  small  proportion  to  its 
convex  area.  The  up2:)er  half  is  coated  with  lamp-black, 
while  the  lower  half  of  the  bulb  is  effectually  protected 
against  loss  of  heat  from  undue  radiation.  The  diminution 
of  energy  attending  the  passage  of  the  sun's  rays  through  the 
lens  is  made  good  by  the  concentration  effected  by  its  cur- 
vature ;  hence  the  true  energy  of  the  radiant  heat  trans- 
mitted will  be  shown  by  the  expansion  of  the  mercury  in 
the  bull).  The  inclination  of  the  lattei",  it  should  be  ob- 
served, promotes  a  rapid  upward  current  of  the  contents  on 
the  top  side,  and  a  corresponding  downward  current  t>n  the 
lower  side,  thereby  rendering  the  indication  prompt  and 
trust\vorthy.  The  water  in  the  surrounding  casing  being 
maintained  at  a  constant  temperature  of.  60°  F.,  it  will  be 
evident  that  the  zero  of  the  thermometric  scale  of  the  actino- 
meter  must  correspond  with  the  line  which  marks  G0°  on 
the  Fahrenheit  scale.  It  scarcely  needs  explanation  that  the 
height  reached  by  the  mercurial  column  after  turning  the 
instrument    to^vards   the    sun   will    be    due   wholly    to    solar 


CHAP.  XXI.        SOLAIi  FABIATIoy  AXD  BIATllEUMAliGY.  321 

eneig}',  since  the  i-adiatiuii  of  tlie  exbaiisted  vessel  toAvartls 
the  bulb  of  the  thermometer  is  only  capable  of  raising  the 
column  to  the  actinometric  zero  (60°  Fahr.)  " 

The  readers  of  Xature  will  remember  that  one  of  my 
articles  reviewed  by  Pere  Secchi  contains  a  demonstration 
accompanied  by  several  diagrams,  proving  that  the  radiant 
heat  emitted  by  the  chromosphere  and  outward  strata  of  the 
solar  envelope  is  inappreciable  at  the  surface  of  the  earth. 
It  will  be  remembered,  also,  that  the  mode  adopted  in  set- 
tling the  fpiestiou  whether  the  solar  atmosphere  is  capable  of 
emitting  heat  rays  of  appreciable  energy  was  that  of  shutting 
out  the  rays  from  the  photosphere  and  collecting  those  from 
the  chromosphere  and  envelope,  in  the  focus  of  a  parabolic 
reflector.  Scarcely  any  heat  being  produced,  notwithstand- 
ing the  great  concentration  l^y  the  reflector,  I  proved  the 
fallacy  of  Pere  Secchi's  remarkable  assumption,  that  the  high 
temperature  at  the  surface  of  the  photosphere  is  caused  by 
radiation  "received  from  all  the  transparent  strata  of  the 
solar  envelope."  It  is  surprising  that,  notwithstanding  the 
completeness  and  positive  nature  of  my  demonstration,  no 
allusion  whatever  is  made  to  the  same  in  a  review  profess- 
ing to  scrutinize  the  subject  critically.  Ignoring  the  evidence 
furnished  by  actual  trial  in  proof  of  the  extreme  feebleness 
of  the  radiating  power,  the  revieAver  proceeds  to  state  "that 
the  outward  strata  might  be  less  hot,  and  that  the  effect 
which  we  measure  is  the  aggregate  of  the  quantities  of  heat 
whicli  are  added,  emanating  from  the  vaiious  transparent 
strata."     Ilow   tlie   outward   coldei'  strata  cause  an  elevation 


332  BADIANT  EEAT.  chap.  xxi. 

of  temperature  by  their  I'adiatiou  toward  tlie  solar  surface  is 
not  explained,  but  reference  is  made  to  tbe  result  of  an  ex- 
periment with  three  small  flames  in  support  of  the  assertion 
that  the  high  temperature  of  10,000,000°  C.  assigned  to  the 
surface  of .  the  sun  is  owing  to  radiation  received  from  all 
the  transparent  strata  surrounding  the  photosphere.  "A  very 
simple  experiment,"  the  reviewer  states,  "  made  at  my  request 
by  P.  Provenzali,  has  shown  that,  if  a  heating  of  2.5  deg. 
can  be  obtained  with  one  flame,  "with  two  flames  placed  one 
before  the  other  4.5  deg.  are  obtained ;  with  three  flames,  5.4 
deg. — a  result  easily  foreseen,  for  everybody  knows  that 
flames  are  transparent." 

My  practical  demonstration  establishing  the  feebleness  of 
the  radiating  power  of  the  matter  composing  the  solar  enve- 
loj^e  having  received  no  considei'ation,  while  the  reviewer,  in 
support  of  his  singular  theory  of  solar  temperature,  points  to 
the  result  of  the  rude  experiment  conducted  by  Pere  Pro- 
venzali, I  have  deemed  it  necessary  to  show  that  the  trans- 
parency of  flames  is  too  imperfect  to  warrant  the  inferences 
drawn. 

The  illustration  on  Plate  32  represents  an  apparatus  by 
means  of  which  the  exact  degree  of  transparency  of  a  series 
of  flames  has  been  ascertained. 

Description :  h,  conical  vessel,  open  at  the  top,  the  bottom 
communicating  with  a  cylindrical  chamber  /  by  a  narrow  pas- 
sage, the  whole  being  enclosed  in  an  exterior  vessel  c,  charged 
with  water  kept  at  a  constant  temperature,  precisely  as  in  the 
actinometer.     A  thermometer  is  applied  near  the  bottom  of 


CHAP.  XXI.        SOLAK  liADIArWX  AND  DIATIIEIiMANOY.  323 

the  cyliiulrieal  chamber,  the  centre  of  the  bulb  coinciding 
with  the  prolongation  of  the  axis  of  the  conical  vessel.  A 
gas-pipe  J,  provided  with  a  series  of  vertical  burners,  is  firmly 
secured  to  an  inclined  table  in  a  position  parallel  to  the  axis 
of  the  conical  vessel.  The  burners  are  provided  with  caps  in 
order  to  admit  of  any  desirable  number  of  jets  being  ignited 
at  one  time,  ^^']len  gas  of  ordinary  pressure  is  admitted  into 
the  pipe  d,  the  side  view  of  the  flame  will  be  as  indicated 
by  the  dotted  lines  at  m  m,  the  thickness  of  each  flame  being 
nearly  0.20  in.,  while  the  width,  shown  by  the  dotted  lines 
?i  11,  somewhat  exceeds  3  ins.  from  point  to  point.  It  will 
be  observed  that  the  prolongation  of  the  axis  of  the  conical 
vessel  upwards  passes  through  the  central  portion  of  the 
flames  at  the  point  of  maximum  thickness  and  intensity. 
Supposing  that  the  instrument  (attached  to  a  table  pro- 
vided with  parallactic  mechanism)  is  directed  towards  the 
sun,  it  will  be  evident  that  all  the  rays  of  a  pencil,  the 
section  of  which  corresponds  with  that  of  the  bulb  of  a 
thermometer,  will  pass  through  the  flames  before  reaching 
the  said  bulb.  Now,  the  temperature  of  the  flames  at  the 
point  pierced  by  the  solar  rays  is  fully  2,000°  F.,  while  the 
actual  intensity  of  the  rays  does  not  exceed  60°.  It  is  hardly 
necessary  to  observe  that  the  illustrated  device  enables  us 
to  ascertain  whether  the  solar  rays  thus  entering  at  a  diffe- 
j-ential  temperature  1,9J:0°  lower  than  that  of  the  incan- 
descent gas  have  their  intensity  augmented  or  diminished 
(luring  the  passage  through  the  heated  medium.  But  before 
we  can  determine  this  question,  it  will  be  necessary  to  ascer- 


324 


BADIAKT  HEAT. 


CHAP.   XXI. 


tain  what  temperature  is  comiimnicated  to  tlie  tliermometer 
by  the  radiant  energy  of  tlie  flames  alone.  Accordingly,  a 
series  of  experiments  have  been  made,  the  result  of  -which 
is  recorded  in  the  annexed  table. 


The  instrument  turned  away  from 
the  sun. 

The  insti-ument  directed  towards  the  sun. 

-a. 

|2i 

1 

i . 

■si 

a 
.1 

III 
as 

Temperature  produced 

by  the  sun's  rays 

acting  directly  on  the 

bulb. 

Temperature  produced 

by  the  sun's  rays 

passing  through  "the 

flames. 

Increment  of 

temperature  attending 

the  passage  of  the  solar 

rays  through  the 

flames. 

Inches. 

°Fah. 

'  Fah. 

'Fah. 

-Fah. 

1 

2 
3 
4 
5 
6 
7 
8 
9 
10 

24.8 
23.8 
22.8 
21.8 
20.8 
19.8 
18.8 
17.8 
16.8 
15.8 

1.76 
2.88 
3.80 
4.58 
5.24 
5.84 
6.38 
6.91 
7.40 
7.90 

21.60 
21.61 
21.62 
21.63 
21.64 
21.65 
21.66 
21.67 
21.68 
21.69 

21.90 
22.20 
22.49 
22.75 
22.99 
23.32 
23.43 
23.63 
23.82 
24.00 

0.30 
0.69 

0.87 
1.12 
1.35 
1.57 
1.77 
1.96 
2.14 
2.31 

The  nature  of  the  investigation  T\dll  be  readily  under- 
stood by  the  following  explanation :  The  instrument  being 
turned  away  from  the  sun  and  the  upper  flame  m  ignited, 
while  the  external  casing  c  is  kept  at  a  constant  temperatui'e 


CHAP.  XXI.        SOLAB  FADTATIOX  AXD  DIATEEBMANOY.  325 

of  60°,  the  coluinii  of  the  thermometer  at  /  slowly  rises  to 
Gl°.70.  The  radiant  heat,  therefore,  of  a  single  Hanie  pro- 
duces a  differential  temperature  of  01°. 70  —  00  =  1°.7G.  The 
second  Hanie  being  ignited,  the  temperature  rises  to  G2°.88, 
thus  increasing  the  differential  temperature  to  2°.88.  The 
ignition  of  the  third  flame  augments  the  differential  tempe- 
rature to  3°.80.  The  remaining  flames  being  ignited  in  regu- 
lar order  downwards,  their  combined  radiant  energy  elevates 
the  temperature  to  G7°.90.  Deducting  the  teniperaturi^  of 
the  enclosure  c  (60°),  the  trial  shows  that,  although  the 
single  flame  at  the  maximum  distance  from  the  bulb  is  capable 
of  producing  a  differential  tempei-ature  of  1''.70,  the  energy 
of  the  ten  flames  together  produces  only  7°.90.  This  fact 
fui-nishes  conclusive  evidence  of  the  imperfect  transparency 
of  the  flames.  Assuming  that  the  heat  rays  are  capable  of 
pas.sing  freely  through  tlie  incandescent  medium,  it  will  be 
perceived  that  the  entii'e  series  of  flames  should  produce  a 
differential  temperature  of  1.76  X  10  =  17''. 6,  showing  a  re- 
tardation of  17.6  —  7.9  =  9°.7.  And  if  we  take  into  account 
the  diminished  distance  of  the  lower  flames  from  the  bulb 
of  the  thermometer,  it  will  ])e  found  that  the  actual  retarda- 
tion greatly  exceeds  this  compntation.  We  have  thus  de- 
monstrated that  flames  are  not  transparent,  as  supposed  l)y 
Pere  Secchi ;  consequently,  the  inferences  drawn  from  the 
experiment  to  which  the  distinguished  savant  refers  in  his 
letter  to  the  French  Academy  of  Sciences  are  Avholly  un- 
wari'nntable. 

Having   disposed    of   the    question    of    transparency,    and 


33G  FADIANT  HEAT.  CHAP.  xxi. 

ascertained  the  degree  of  temperature  commimicated  to  the 
tliermometer  by  tlie  radiant  energy  of  tlie  flames  alone,  let 
us  now  suppose  that  the  instrument  has  been  turned  towards 
the  sun.  The  temperature  produced  by  the  combined  energy 
of  solar  radiation  and  the  radiation  of  the  flames,  after  direct- 
ing'' the  instrument  towards  the  luminary,  will  be  found  I'e- 
corded  in  the  fifth  column  of  the  table.  Dispensing  with  a 
detailed  record  of  the  energy  transmitted  for  each  flame 
separately,  let  us  at  once  consider  the  effect  produced  by 
passing  the  sun's  rays  through  the  entire  series.  It  has 
already  been  stated  that  the  radiation  of  all  the  flames  com- 
bined imparts  a  differential  temperature  of  7°.90  to  the 
thermometer.  By  reference  to  the  table,  it  will  be  seen  that 
the  temperature  produced  by  the  sun's  rays  is  21°.69  when 
the  flames  are  extinguished.  Consequently,  the  temperature 
produced  after  lighting  the  whole  series  ought  to  be  21.69 
+  7.90  =  29°.59  instead  of  24°. 00,  since  solar  heat,  under 
analogous  conditions,  is  capable  of  increasing  the  temperature 
of  substances,  whatever  be  their  previous  intensity.  Our 
experiment,  therefore,  furnishes  additional  evidence  of  the 
imperfect  transparency  of  flames.  But  notwithstanding  this 
want  of  transparency,  it  will  be  found  on  referring  to  the 
table  that  an  augmentation  of  temperatui'e  of  24.00  —  21. G9 
=  2°.31  takes  place  while  the  comparatively  cold  solar  rays 
pass  through  the  incandescent  medium.  This  exti'aordinary 
fact  points  to  an  increase  of  molecular'  energy  within  the 
incandescent  gas,  although  its  temperature  is  fully  1,900° 
higher  than  the  intensity  of  the  sun's  rays. 


CHAPTER  XXII. 

CONSTANCY  OF  ROTATIOX  OF  THE  EARTH  INCOMPATIBLE 
WITH  SOLAR  INFLUENCE. 


Laplace's  demonstration,  showing  that  the  axial  rotation 
of  the  eartli  is  not  affected  by  atmospheric  currents  and 
similar  motions  caused  by  solar  heat,  has  been  accepted  by 
physicists  as  incontrovertible.  The  German  mathematician, 
Dr.  Mayer— celebrated  for  his  demonstration  establishing  the 
equivalent  of  heat— says  in  a  discourse  on  that  branch  of 
celestial  mechanics  which  relates  to  the  effect  produced  by 
contrary  atmospheric  currents :  "  The  final  result  of  the  ac- 
tion of  these  opposed  influences  is,  as  regards  the  rotation  of 
the  earth,  according  to  well-known  mechanical  principles  =  0 ; 
for  these  currents  counteract  each  other,  and  therefore  cannot 
exert  the  least  influence  on  the  axial  rotation  of  the  earth. 
This  important  conclusion  was  proved  by  Laplace."  "The 
same,"  he  adds,  "holds  good  foi-  eveiy  imaginable  action 
which  is  caused  by  the  radiant  heat  of  the  sun,  or  by  the 
heat   which   reaches   the    surface   from   the    earth's    interior, 


338  EADIAKT  HEAT.  chap.  xxii. 

A\lietlier  the  action  be  in  the  aii',  in  the  water,  or  on  the 
land.  The  effect  of  every  single  motion  produced  by  these 
means  on  the  rotation  of  the  globe  is  exactly  compensated  by 
the  effect  of  another  motion  in  an  oj^posite  direction,  so  that 
the  resultant  of  all  these  motions  is,  as  far  as  axial  rotation  of 
the  globe  is  concerned,  =  0."  I  propose  to  show  that  this  con- 
clusion is  fallacious,  and  that  the  sun's  radiant  heat  develops 
forces  capable  of  diminishing  perceptibly  the  earth's  rotary 
velocity ;  and  that  unless  the  retarding  influences  of  solar 
heat,  the  existence  of  which  I  am  going  to  establish,  are 
counteracted  by  some  cosmical  force  of  which  we  have  no 
knowledge,  the  earth's  rotary  velocity  will  be  considerably 
reduced  in  the  course  of  time. 

There  are  two  classes  of  force  produced  by  solar  heat, 
capable  of  retarding  the  axial  rotation,  differing,  however, 
entirely  as  regards  ultimate  results.  The  first  class  includes 
animate  exertion,  mechanical  force  produced  by  heat  de- 
veloped by  the  combustion  of  organic  substances,  and  the 
resistances  of  abraded  solid  matter  transferred  from  its  ori- 
ginal position  by  the  waters  of  rivers  flowing  towards  the 
equator.  The  forces  thus  enumerated,  it  will  be  shown,  retard 
the  rotary  velocity  of  the  globe  in  all  cases  when  they  remove 
weight  to  a  greater  distance  from  the  axis  of  rotation,  i.e., 
expand  the  circle  of  gyration,  thereby  diminishing  the  num- 
ber of  revolutions  performed  in  a  given  time.  Obviously, 
the  vis  viva  of  the  rotating  mass  Avill  remain  iTudiminished, 
as  the  centre  of  gyration  is  merely  removed  to  a  greater 
distance  from  the   axis  of   rotation.     Accordingly,   the    axial 


CHAP.  XXII.  THE  EAETU-S  AXIAL  ROTATION.  329 

rotation,  though  checked,  cau  never  be  stopped  by  the  class 
of  retarding  influences  thus  pointed  out.  The  second  class, 
however — which  comprises  the  retardation  produced  by  the 
atmospheric  air  during  its  course  from  the  polar  to  the  e(pia- 
torial  regions,  and  the  retardation  caused  by  the  waters  which 
flow  towards  the  equator  to  restore  the  quantity  lost  by  the 
powerful  evaporation  within  the  tropics — not  only  diminishes 
the  rotary  velocity,  but,  at  the  same  time,  deprives  the  earth 
of  so  creat  an  amount  of  vis  viva  that  the  axial  rotation 
must  ultimately  cease,  unless  some  exterior  compensating 
force  exists — a  supposition  at  variance  ^nth  the  principles  of 
mechanics. 

Let  us  now  briefly  examine  the  nature  of  the  retarding 
influences  of  the  first-named  class,  which,  as  stated,  are  un- 
attended by  any  loss  of  the  earth's  vis  viva — namel)',  animate 
force  and  mechanical  energy,  resulting  fi'om  the  combustion 
of  organic  substances  when  expended  in  raising  weight  to 
remain  permanently  in  an  elevated  position ;  and  the  retarda- 
tion caused  by  solid  matter  carried  towards  the  equator. 
Before  entering  on  this  examination,  it  will  be  instinctive  to 
test  by  some  familiar  illustration  the  correctness  of  Mayer's 
assumption,  that  "every  imaginable  action  affecting  the  rota- 
tion of  the  globe  is  exactly  compensated  by  the  effect  of 
another  motion  in  an  opposite  direction."  A  great  variety  of 
instances  might  be  mentioned  in  which  the  development  of 
mechanical  energy,  productive  of  heat,  counteracts  the  rotary 
motion  of  the  earth,  and  deprives  it  permanently  of  a  certain 
amount   of    vis  viva.      Suppose,   for   instance,   a    locomotive 


330  BADIANT  HEAT.  chap.  xxii. 

train  weigliing  400  tons  to  be  started  from  the  Mestern 
terminus  of  a  railway  running  from  west  to  east.  Suppose, 
also,  that  when  this  train  has  acquired  a  velocity  of  50  ft. 
per  second,  it  encounters  another  similar  train  which  is  at 
rest.  The  result  of  such  an  encounter,  in  a  dynamic  point 
of  vie^v,  is  now  Avell  understood.  Apart  from  a  small  amount 
of  energy  absorbed  in  overcoming  the  cohesive  force  between 
the  particles  composing  the  materials  fractured  by  the  con- 
cussion, the  encounter  will  develop  an  amoimt  of  heat 
corresponding  with  the  vis  viva  of  the  arrested  train.  It 
scarcely  needs  explanation  that  in  putting  the  train  in  motion 
from  the  terminus  eastward  the  rails— /.(>.,  the  surface  of  the 
earth — will,  in  consequence  of  the  adhesion  between  the 
wheels  and  the  rail,  be  pushed  westward ;  hence  in  a  direc- 
tion contrary  to  the  earth's  rotation.  The  amount  of  dynamic 
energy  which  the  train  thus  imparts  to  the  earth  in  an  oppo- 
site direction  to  that  of  rotation  may  be  readily  ascertained 
by  multiplying  the  arrested  weight  by  the  height  necessary 
to  produce  a  velocity  of  50  ft.  per  second — namely,  39  ft. ; 
hence  400  X  2,240  X  39  =  34,944,000  foot-pounds.  Deduct- 
ing the  small  amount  of  energy  Avhieh  favors  the  earth's 
rotation  called  forth  by  the  rolling  friction  and  adhesion  of 
the  wheels  of  the  stationary  train,  during  the  short  retro- 
grade motion  attending  the  concussion,  it  will  be  found  that 
the  earth  loses  an  amount  of  vis  viva  of  fully  34,000,000 
foot-pounds.  The  assumption  of  Dr.  Mayer,  based  on  the 
theory  of  Laplace,  that  the  resultant  of  all  imaginable  mo- 
tions as  regards   the  earth's  axial  rotation   is  =  0,  has  thus 


CHAP.  XXII,  THE  EAliTWS  AXIAL  L'OTATIOK.  331 

been  proved  to  be  untenable.  It  is  not  intended  to  question 
Laplace's  conclusion  as  regards  the  existence  of  a  compen- 
sating effect;  he  was  mistaken  only  as  to  its  nature — a  mis- 
take, however,  of  ijaraiiuniiit  importance,  as  we  have  shown 
that  the  compensation  for  the  lost  energy,  in  the  case  pre- 
sented, is  the  generation  of  a  certain  amount  of  heat  Avhich, 
in  less  than  three  hours  after  the  concussion,  if  the  sky  be 
clear,  radiates  into  space,  leaving  the  earth  minus  34,000,000 
foot-pounds  of  vis  viva.  The  important  fact  should  not  be 
overlooked  that  the  retardation  thus  established  is  the  result 
of  solar  energy  stored  in  the  combustibles  of  the  locomotive 
furnace.  Numerous  instances  of  a  similar  nature  micrht  be 
mentioned  in  support  of  the  assertion  that  the  earth  is  sub- 
jected to  retarding  influences  and  loss  of  vis  viva  by  me- 
chanical motions  on  the  earth's  surface  \vhich  result  in  the 
production  of  heat  radiated  into  space.  But  all  these  are 
insignificant  compared  with  the  stupendous  amount  of  retarda- 
tion caused  by  the  conversion  of  mechanical  energy  into  heat 
within  the  opposing  atmospheric  currents  circulating  between 
the  equatorial  and  polar  regions.  In  connection  with  this 
proposition,  it  will  be  proper  to  remark  that  our  knowledge 
of  the  convertibility  of  mechanical  energy  and  heat — in  other 
words,  the  convertibility  of  mechanical  and  molecular  energy 
— has  completely  upset  Laplace's  demonstration,  on  which 
physicists  have  based  their  assumption,  that  the  rotaiy 
velocity  of  the  earth  cannot  be  affected  by  the  sun's  radiant 
heat. 

Let  us  now  examine,  separately,  those  forces  produced  by 


333  BABIANT  HEAT.  chap.  xxii. 

solar  lieat  wliicli  tend  to  check  tlie  earth's  rotary  velocity 
by  removing  weight  from  the  axis  of  rotation — i.e.,  expanding 
the  circle  of  gyration — and  those  vt^hich  occasion  a  diminution 
of  the  rate  of  axial  rotation  without  disturbing  the  balance 
of  the  rotating  mass.  The  first  class :  Animate  or  muscular 
enei'gy,  and  the  force  generated  by  heat  from  the  combustion 
of  organic  matter,  controlled  by  the  hiiman  mind,  both  re- 
sulting indirectly  from  the  sun's  radiant  heat.  That  the  hand 
and  intellect  of  men  have  caused  a  disturbance  of  the  position 
of  the  earth's  centre  of  gp-ation  will  be  deemed  a  startling 
assertion,  yet  it  cannot  be  controveiied  in  view  of  the  fol- 
lowing facts.  The  millions  of  tons  of  matter  contained  in 
the  Pyramids,  removed  to  a  greater  distance  from  the  axis 
of  rotation  by  the  muscular  exertion  of  the  ancient  Egyptians, 
disturbed  the  previous  balance  of  the  rotating  mass,  causing 
a  tendency  to  check  the  earth's  rotary  velocity  and  to  increase 
the  length  of  day.  Nor  can  it  be  questioned  that  if  London 
had  not  been  built,  and  if  the  building  materials  of  Paris  yet 
remained  in  the  Catacombs,  the  sun  would  rise  earlier  than 
it  now  does,  though  the  diifereuce  woiild  be  small  beyond 
computation.  The  aggregate  of  the  weight  removed  from 
below,  and  piled  above  the  crust  of  the  globe  by  the  hand 
of  man,  is,  however,  so  great  that  figures  are  competent  to 
express  the  extent  of  the  consequent  retai'dation  of  the  axial 
rotation,  while  the  divisions  of  our  common  instruments  for 
measuring  distance  are  sufficiently  minute  to  indicate  the 
expansion  of  the  earth's  circle  of  gyration  caused  by  the 
transfer  of  matter  under  consideration.     A  first-class  modern 


CHAP.  XXII.  TEE  EAETU'S  AXIAL  BOTATION.  333 

cit}',  for  instance,  contains  upwards  of  100,000  bouses;  each 
house  contains  on  an  average  400  tons  of  mineral  matter ; 
hence  the  total  weight  of  brick,  earth,  or  stone  removed  fi-om 
below  the  surface  to  a  considerable  height  above  the  earth's 
surface  exceeds  40,000,000  tons — a  mere  fractidu  compar('d 
with  the  weight  of  the  whole  of  human  hal)itations  and 
other  stnictures  raised  above  the  surface  of  the  earth  chiefly 
by  muscular  eifort.  Let  us  add  the  weight  of  materials 
raised  from  mines  to  an  increased  distance  from  the  axis  of 
rotation,  by  animate  exertion  and  by  mechanical  force  con- 
trolled by  intellect. 

An  element  of  greater  importance,  connected  with  the 
fii-st  class  of  retarding  influences  produced  by  the  sun's  ra- 
diant heat,  next  claims  our  attention — namely,  the  solid  and 
sedimentaiy  matter  detached  by  the  abrasion  of  i-ain-water, 
and  afterwards  conveyed  by  the  currents  of  rivers  to  a  po- 
sition nearer  the  equator ;  hence  removed  to  a  greater  dis- 
tance from  the  axis  of  rotation.  The  question  whether  any 
estimate  can  be  made  of  the  aggregate  weight  of  matter, 
the  original  position  of  which  is  being  changed  during  defi- 
nite periods  by  the  caiise  referred  to,  is  by  no  means  so 
ditticult  to  answer  as  might  appear  without  due  considera- 
tion. It  is  tnie,  we  do  not  know  what  quantity  of  water 
or  sediment  is  carried  towards  the  equator  by  the  several 
rivei"s;  but  we  can  compute  with  sutficient  exactness  the  ex- 
tent of  the  river  basins.  Accordingly,  if  we  could  estab- 
lish a  mean  of  discharge  per  square  mile  of  some  very 
extensive  basin    comprising  all   the   varieties  of   climate  and 


334  BADIANT  HEAT.  chap.  xxii. 

soil,  tlie  question  could  be  satisfactorily  answered.  Fortu- 
nately, one  of  tlie  longest  rivers  on  tlie  globe,  the  Missis- 
sippi, wliicli  drains  tlie  greatest  extent  of  sui-face  witb  but 
two  important  exceptions,  Las  been  carefully  surveyed  by  a 
corps  of  Topograpliical  Engineers,  by  order  of  tlie  United 
States  Government.  Not  only  lias  this  great  river  been 
thus  carefully  examined,  but  the  basin  it  drains  comprises 
ex^ery  variety  of  soil  and  climate — its  source  being  among 
sno\vs  and  lakes  frozen  during  the  greater  portion  of  the  year, 
while  the  outlet  is  near  the  tropics.  That  the  Mississippi 
basin  represents  the  average  of  the  liver  systems  of  both 
hemispheres  has  been  established  by  the  fact  that,  although 
the  rain-gauges  at  its  northern  extremity  show  only  13  ins. 
for  twelve  months,  those  of  its  southern  boundary  reach 
66  ins.,  with  every  possible  gradation  of  jwecipitatiou  in  the 
intermediate  space.  In  addition  to  this  important  circum- 
stance, the  basin  covers  21  deg.  of  latitude  and  35  deg.  of 
longitude,  or  1,460  miles  by  1,730  miles ;  hence  comprising 
an  area  greater  than  the  entire  European  Continent  west  of 
the  rivers  Vistula  and  Pruth.  It  may  be  confidently  as- 
sumed, therefore,  that  the  Mississippi  basin  represents  the 
average  discharge  of  Avater  and  sediment  so  nearly  that  cal- 
culations based  thereon,  applied  to  the  river  systems  of 
botli  hemispheres — excepting  some  of  the  northern  Asiatic 
and  American  livers — will  exhibit  a  general  result  differing 
but  slightly  from  what  would  be  established  if  each  river 
had  been  examined. 

The  elaborate   repoi't   of  General  Humphreys  to  the  Bu- 


CUAP.  XXII.  THE  EAirrWS  AXIAL  liOTATlON.  335 

reau  of  Topographical  Eugiueers,  AVasliington,  shows  that 
the  average  quantity  of  earthy  matter  carried  into  the  Gulf 
of  ]\Iexico,  partly  suspended  in  the  water  and  partly  pushed 
along  the  bottom  of  the  river  by  the  current,  amounts  for 
each  twelve  months  to  903,100  millions  of  pounds.  This 
enormous  weight  of  matter  is  contributed  l>y  numerous 
large  branches  and  upwards  of  1,000  small  tributaries.  The 
mean  distance  of  the  streams  along  which  the  sediment  is 
carried  in  its  course  to  the  sea  exceeds  1,500  miles.  The 
distance  which  determines  the  amount  of  force  tending  to 
check  the  earth's  rotation  is,  howevei',  cousidei'ably  shorter. 

The  maps  of  the  Mississippi  River  basin  accompanying 
the  report  referred  to  show  that  its  centre  is  situated  7  deg. 
10  min.  west  of  the  mouth  of  the  main  river,  and  11  deg. 
15  min.  north  of  the  same,  in  latitude  40  deg.  15  min.  It 
will  be  found  on  inspecting  the  section  of  the  earth  (see 
PI.  33)  that,  agreeably  to  the  stated  Latitude,  the  centre 
of  the  Mississippi  basin  rotates  in  a  circle  of  15,784,782  ft. 
radius ;  hence  its  velocity  round  the  axis  of  the  globe  is 
1,147.90  ft.  per  second.  The  month  of  the  river,  it  will  be 
found  on  calculation,  rotates  in  a  circle  of  18,246,102  ft. 
radius,  with  a  circumferential  velocity  of  1,326.89  ft.  per 
second.  Comparing  these  velocities,  it  ^\ill  be  seen  that  an 
increased  circumferential  velocity  of  178.99 — say  179 — ft. 
per  second  is  imparted  to  the  water  and  to  the  sediment- 
ary matter  w^hich  it  conveys  during  the  course  from  the 
centre  of  the  basin  to  the  mouth  of  the  ii\er.  As  l)efore 
stated,  the  annual  discharge   of   earthy  matter  at  the  mouth 


o.]G  EABIAM  UEAT.  chap.  xxii. 

of  the  river  is  903,100  millions  of  pounds.  The  centre  of 
the  basin^lat.  40  deg.  15  min. — being  2,401, oi'O  ft.  nearer 
to  the  axis  of  rotation  than  the  mouth  of  the  river  iu  lat. 
20  deg.  0  min.,  it  will  be  found  that  tlie  increase  of  rotary 
velocity  is  179  ft.  per  second,  as  already  stated — a  rate  ac- 
quired by  a  fall  of  500.6  ft.  The  elements  are  thus  fur- 
nished for  determining  with  exactness  the  amount  of 
retardation  attending  the  change  of  position  of  the  abraded 
matter  during  its  transfer  from  the  basin  to  the  mouth  of 
the  river.  Multi2->lying  903,100  millions  l)y  500.6,  Ave  ascer- 
tain that  the  counteracting  force  amounts  to  452,000,000,- 
000,000  foot-pounds  annually  =  452  X  10"  foot-pounds  in  a 
century.  The  earth's  present  vis  viva  being  18,875,361  X 
10''  foot-pounds  (to  be  demonstrated  hereafter),  it  is  easy  to 
calculate  that  the  retardation  occasioned  by  the  stated  re- 
acting energy  called  forth  by  the  sedimentary  mattei'  which 
is  carried  to  the  ocean  by  the  Mississippi  will  amount  to 
lu^^oo  of  a  second  in  a  century.  In  view  of  this  small  frac- 
tion of  time,  it  will  be  well  to  remind  the  reader  that  the 
retardation  of  the  earth's  rotary  velocity,  inferred  from  the 
apparent  acceleration  of  the  moon's  mean  motion,  now  gene- 
rally admitted  by  astronomers,  is  somewhat  under  12  seconds 
in  a  century.  Insignificant  as  this  retardation  appears  to  be, 
it  calls  for  a  constant  reacting  force  of  455,000,000,000  foot- 
pounds per  second,  as  will  be  shown  in  the  course  of  our  in- 
vestigation. Dividing  this  amount  by  the  adopted  standard 
of  a  horse-power — viz.,  550  foot-pounds  per  second — it  will 
be  found  that  a  constant   energy  represented  by  827,000,000 


CHAP.  XXII.  THE  EAinir^  AXIAL  nOTATION.  337 

horse-po\yer,  exerted  in  a  contrary  direction  to  that  of  rota 
tion,  is  necessary  to  check  the  rotary  motion  to  the  extent 
mentioned — viz.,  sUs^  —  tsW  of  a  revolution  in  the  course 
of  a  century.  Accordingly,  720,000  years,  nearly,  ^\  ill  elapse 
before  one  entire  revolution  shall  liave  been  lost,  notwith- 
standing the  existence  of  a  constantly  retarding  force  of 
455,000  niillions  of  foot-pounds  per  second.  M'e  can  i-cadily 
ascertain  the  aggregate  of  this  force  during  the  long  period 
mentioned,  if  we  multiply  the  same  by  the  number  of  revo- 
lutions of  the  earth  per  annum,  alid  tlie  number  of  seconds 
for  each  revolution  ;  thus,  455  X  10"  X  365.24  X  86,400  X 
720,000  =  103,379,867  X  10"  foot-pounds.  By  dividing  this 
amount  of  energy  in  the  earth's  vis  viva,  18,875,361  X  10"' 
foot-ponnds,  we  ascertain  that  the  stated  enormous  retarda- 
tion overcome  in  the  course  of  720,000  years  amounts  to 
only  ts\ts  of  the  present  rotary  vis  viva  of  our  jjlanet.  Pro- 
liably  no  other  mode  of  presenting  the  subject  could  give 
so  clear  an  idea  of  the  vastness  of  the  mechanical  energy 
developed  by  the  axial  rotation  of  a  sphere  8,000  miles  in 
diameter,  whose  specific  gravity  is  2\  times  that  of  granite, 
revolving  at  a  rate  of  one  revolution  in  24  hom*s.  Let  us 
bear  in  mind  that  the  retardation  produced  by  the  sedi- 
mentaiy  matter  carried  to  the  Gulf  of  ]\Iexico  by  the  ^lissis- 
sippi,  and  the  precipitation  which  causes  the  abrasion  of  the 
solid  matter  and  the  currents  by  which  it  is  conveyed,  are 
the  direct  results  of  the  sun's  radiant  heat. 

\\\\\\    reference    to    the    taldes    (see    pages    342-353),    it 
sliould    be   stated    that    the    amounts   of   the    retarding  force 


338  BABIANT  HEAT.  chap.  xxii. 

entered  in  the  last  two  columns  but  one  are  based  on  tbe  data 
furnished  by  the  examinations  of  the  great  Western  river — viz., 
that  1  lb.  of  solid  matter  and  1,350  lbs.  of  water  per  second 
are  carried  to  the  sea  for  every  40.08  sq.  miles  of  basin. 
All  other  particulars  necessary  in  computing  the  retarding 
energy  exerted  by  each  river,  separately  for  the  two  hemi- 
spheres, will  be  found  in  the  tables.  The  mode  adopted  in 
determining  the  area  drained  by  each  river  and  tributaries 
will  be  readily  comprehended  by  the  following  explanation  : 
The  extent  of  the  several  river  basins,  136  in  all  in  both 
hemispheres,  has  been  ascertained  from  the  best  maps  extant ; 
the  boundaries  of  the  basin  being  determined  by  drawing 
a  line  on  the  map,  and  dividing  the  territory  equally  be- 
tween the  source  of  each  river  and  tributaries  and  those  of 
adjoining  basins.  The  boundaries  being  thus  defined,  the 
areas  have  been  calculated  in  English  statute  miles ;  the 
latitude  and  longitude  of  the  centre  of  each  basin  being  de- 
termined at  the  same  time.  By  supposing  the  earth  to  be  a 
perfect  sphere  7,912.41  miles  in  diameter,  according  to  Sir 
John  Herschel's  determination,  the  calculations  have  been 
rendered  extremely  simple.  This  will  be  seen  by  reference  to 
the  section  of  the  earth  before  referred  to,  which  contains 
all  the  elements  for  computing  the  rotary  velocity  of  the 
centres  of  the  river  basins  and  of  the  outlets  of  the  rivers. 
These  velocities  have  been  entered  in  the  tables  separately 
for  each  river  basin;  also  the  retardation,  expressed  in  foot- 
pounds per  second,  caused  by  the  increase  of  rotary  velocity 
during  the  transfer  of  the  sedimentary  matter  from  the  cen- 


CH  A  I".  XXII.  THE  EAinWS  AXIAI.  liOTATION.  339 

tre  of  the  basiu  to  tlie  luoutli  of  the  river.  The  last  coluinn 
but  one  of  the  tables  contains  the  result  of  computations  of 
the  amount  of  retardation  occasioned,  by  the  volume  of  water 
which  conveys  the  sedimentary  matter — a  subject  to  be  con- 
sidered under  a  separate  head  hereafter. 

It  should  be  observed  that,  o\ving  to  their  trifling  in- 
fluence on  the  earth's  rotation,  and  in  order  to  save  space, 
all  the  Englisli  and  Scotch  river  basins  whose  sediment  is 
transferred  in  the  direction  of  the  equator  have  been  en- 
tered together  in  the  tables ;  the  rivers  of  Ireland  likewise. 
But  in  computing  the  loss  or  gain  of  energy,  each  river 
basin  has  been  calculated  by  itself,  the  amount  of  retarda- 
tion entered  being  the  result  of  the  whole  quantity  of  sedi- 
ment transferred  towards  the  equator  by  the  several  small 
basins  referred  to.  Accordingly,  the  area  which  is  entered 
in  the  table  represents  the  total.  The  river  basins  of 
Sweden  and  Norway,  being  very  numerous  and  unimportant, 
have  also,  in  some  districts,  been  entered  together  in  tlie 
tables  like  those  of  Great  Britain.  Finally,  the  narrow- 
coast  districts,  in  both  hemispheres,  have  been  computed 
and  inserted  in  the  table  in  a  similar  manner. 

The  quantities  of  sedimentary  matter  discharged  by  the 
Indus,  Ganges,  and  Brahmapooti-a,  being  known  with  toler- 
able accuracy  from  actual  observation,  have  not  been  com- 
puted according  to  the  standard  furnished  by  the  Mississippi, 
which,  as  before  stated,  is  1  lb.  of  sediment  per  second  for 
every  40.08  sq.  miles  of  basin.  Besides,  local  circumstances, 
sucli  as  the  heated    waters  and    profuse    evaporation    of   the 


340  RADIANT  BEAT.  CHAP.  xxil. 

Bay  of  Bengal,  and  the  powerful  condeusatiou  attending 
the  close  vicinity  of  the  Himalaya  Mountains,  render  the 
Gauges  quite  exceptional. 

Respecting  the  African  rivers,  none  of  which  have  been 
entered  in  the  tables,  it  may  be  briefly  stated  that  they 
luive  no  material  influence  on  the  earth's  rotation,  from  the 
fact  that  the  two  principal  rivers,  the  Nile  and  the  Niger, 
flow  in  opposite  directions — the  former  towards  the  pole 
and  the  latter  towards  the  equator.  There  is,  however, 
considerable  dift'ereuce  of  latiti;de,  productive  of  an  in- 
creased retarding  influence  of  the  Nile  ;  but  this  cannot  be 
far  from  balanced  by  the  greater  quantity  of  sedimentary 
matter  brought  down  by  the  Niger,  as  pi'oved  by  its  delta 
of  240  miles  of  coast.  The  general  course  of  the  other  im- 
portant rivers  of  Africa — the  Senegal,  Zambesi,  and  the 
Oi'ange  River — is  so  nearly  parallel  with  the  equator  that 
they  exercise  no  appreciable  influence  on  the  axial  rotation 
of  the  earth. 

Australia,  being  drained  by  rivers  the  courses  of  which 
are  directed  to  all  points  of  the  compass,  consequently  exer- 
cising no  appreciable  influence  as  regards  the  earth's  i-otary 
motion,  has  likewise  been  excluded  from  the  tables.  It 
should  be  observed  that  the  basin  of  the  important  river 
Goolwa  and  its  tributaries  (excepting  the  Callewatta)  is 
almost  on  the  same  parallel  with  the  mouth  of  the  main 
river;  hence  scarcely  any  retarding  force  is  produced,  uot- 
Avithstanding  the  great  extent  of  basin  drained  by  the 
Goolwa.     The  Amazon,  which    drains    more    than    two    mil- 


CHAP    XXII.  THE  EAETirS  AXIAL  ROTATION.  341 

limis  of  Siiuare  miles,  strikingly  illustrates  the  trifling  in- 
tlueuce  on  the  earth's  rotary  velocity  of  rivers  the  centres 
of  whose  basins  are  nearly  on  the  same  parallel  \vith  their 
outlets,  the  enormous  mass  of  solid  matter  carried  to  the 
ocean  by  this  river — the  greatest  ou  the  globe — exerting  a 
retarding  influence  of  only  70,000  foot-pounds  per  second. 

The  asrorreorate  of  solid  matter  removed  from  its  orii^inal 
position  by  the  river  S3'stems  of  both  hemispheres,  and  carried 
towards  the  equator — consecpiently  removed  to  a  greatei'  dis- 
tance from  the  axis  of  rotation — exerts,  as  shown  by  the 
tables,  a  retai-ding  influence  of  39,894,658  foot-pounds  per 
second.  If  we  multiply  this  amount  by  86,400  seconds,  we 
learn  that  for  each  revolution  the  earth  has  to  overcome 
a  retarding  energy  represented  by  3,4-46,898,451,200  foot- 
pounds ;  l^ut  the  effect  of  this  retardation  as  regards  the 
length  of  the  century  cannot  be  properly  considered  until  we 
have  investigated  the  second  class  of  force  before  adverted 
to,  viz.,  that  force  which  destroys  tlie  earth's  vis  viva  Avith- 
out  disturbing  the  position  of  its  centre  of  gyration.  We 
have,  however,  proceeded  far  enough  with  our  investigation 
to  show  the  fallacy  of  the  accepted  doctrine  of  compensation 
lelative  to  the  energies  which  affect  the  earth's  rotary  velo- 
city. We  have  clearly  shown  that  constancy  of  rotation  of 
the  earth   is  incompatible  with  solar  influence. 


349 


BAD  J  ANT  HEAT. 


CHAP.  XXII. 


elvers  flowing  towards  the  equator. 
Hemisphere. 


Eastern 


Name  op  Rivee  oe  Disteict. 


Anadir , 

N.  W.  coast  Sea  of  Kamtschatka 

Penshina 

W.  coast  Sea  of  Okhotsk 

Yama 

Tawi  and  Kowa 

Ochola 

Ud 

Tollmen 

Yaloo 

Sira  Muren 

Chanton 

Pei-ho 

Min  Kiang 

Han  Kiang 

Tcke  Kiang 

Hoang  Ho 

Sang  Koi 

Coast  Eivers,  Gulf  of  Tonqnin 

Menam  Kong 

Irawady 

Bralimapootra 

Ganges  above  Gliazepoor 

Ganges  below  Gliazepoor 


Rivee  Basin. 


Area. 


Sq.  MUm. 


119,200 

52,000 

50,100 

32,600 

15,500 

13,300 

21,500 

25,400 

20,000 

21,200 

78,700 

29,800 

124,000 

25,400 

26,200 

144,400 

448,200 

76,300 

26,000 

329,500 

205,000 

379,000 

187,100 

237,200 


Deg.  M. 


65  50 
6142 
63  20 
62  00 
60  45 
60  25 
60  48 
55  25 
43  20 

41  10 

42  40 
41  00 
38  40 

26  20 
24  18 
24  10 
36  50 
22  40 
20  12 
16  38 
22  35 
29  12 

27  25 
27  30 


East 

of 
outlet. 


Deg.  M. 


0  10 
0  20 


05 


05 


05 


West 

of 
outlet. 


135 


0  05 
130 
0  10 
0  40 
2  35 

0  15 

1  06 

0  30 

2  45 

1  15 

3  50 
10  25 

2  28 
150 

3  15 
0  30 

5  25 
5  12 


622 

720 

681 

713 

742 

750 

741 

8G2 

1,105 

1,144 

1,117 

1,146 

1,186 

1,362 

1,384 

1,386 

1,216 

1,402 

1,426 

1,455 

1,403 

1,326 

1,346 

1,347 


3 

4 
5 
6 

7 
8 

9 

lO 

II 

12 
13 

■4 
IS 
16 

17 
18 

19 

20 
21 
22 

23 
•24 


CHAP.   XXII. 


THE  EAh'TWS  AXIAL  DOTATION. 


343 


2 

3 
4 
5 
6 

7 
8 

9 

10 

II 

12 

13 

14 
15 
i6 

17 
i8 

19 
20 
21 
22 
23 
24 


Rivers 

FLOWING    TOWARDS 

THE  Equator. 

Eastern 

Hemisphere. 

Mouth  of  Kiveb, 

Retardation. 

■§ 

5"^ 

i  -§* 

3 

3 

1  1 

By  sediment 

By  water. 

Total. 

Deg.  if. 

Fett  ptr 
etcond. 

Feet  per 
second. 

Foot-pounds  per 
teoond. 

Foot-pound t  per  teoond. 

Foot-povnde  per  tecond. 

64   30 

054 

32 

47,680 

64,368,000 

64,415,680 

GO  45 

742 

22 

9,828 

13,267,800 

13,277,628 

61  46 

719 

38 

28,256 

38,145,600 

38,173,856 

61  20 

729 

16 

3,260 

4,401,000 

4,404,260 

59  40 

767 

25 

3,786 

5,111,100 

5,114,886 

59  40 

767 

17 

1,503 

2,029,050 

2,030,553 

59  45 

765 

24 

4,838 

6,-531,300 

6,536,138 

55  20 

864 

2 

40 

54,000 

54,040 

42  65 

1,112 

7 

.  385 

519,700 

520,085 

40  10 

1,161 

17 

2,396 

3,234,600 

3,236,996 

40  50 

1,149 

32 

31,480 

42,498,000 

42,529,480 

39  10 

1,178 

32 

11,920 

16,092,000 

16,103,920 

38  25 

1,187 

1 

48 

64,800 

64,848 

26  00 

1,364 

2 

40 

54,000 

54,040 

23  20 

1,395 

13 

173 

233,550 

233,723 

22  53 

1,399 

13 

9,530 

12,865,500 

12,875,030 

33  45 

1,263 

47 

386,797 

522,175,950 

."^22, 502,747 

20  32 

1,423 

21 

13,143 

17,743,050 

17,756,193 

20  00 

1,427 

1 

10 

13,500 

13,510 

10  Co 

1,496 

41 

216,399 

292,138,650 

292,355,049 

16  10 

1,459 

56 

251,125 

339,018,750 

339,269,875 

22  00 

1,408 

82 

5,187,040 

7,002,504,000 

7,007,691,040 

22  00 

1,408 

62 

1,463,818 

1,976,154,300 

1,977,0!8,1]8 

22  UO 

1,408 

61 

2,694,633 

3,637,754,550 

3,640,449,183 

344 


BABIANT  HEAT. 


CHAP.  XXII. 


Rivers  flowing  towards  the  Equator.     Eastern 
Hemisphere. 


Name  of  River  or  District. 


EiVER  Basin. 


Area. 


Sq.  Miles. 


Dig.  M. 


East 

of 
outlet. 


West 

of 
outlet. 


Deg.  it 


fc-.t 


Khaladaing 

Braining  and  Coyli' 

Maliannddy 

N.  W.  coast  Bay  of  Bengal . . . . 

Godavery 

Kislina 

W.  coast  Bay  of  Bengal 

Penaar 

Palar 

Cauvery 

Tapty 

Nurbndda 

Sukernnlly 

Jahu 

Indns 

Helmund 

N.  coast  of  Arabi;in  Sea.. ...... 

N.  E.  coast  of  Persian  Gulf.  .  .  . 

S.  coast  of  Arabia 

Euphrates  and  Tigris 

Kour 

Oural 

Don 

Emba  district 


27,400 

31,000 

41,300 

24,000 

133,000 

104,900 

8,300 

17,900 

23,700 

25,000 

23,600 

21,600 

29,700 

48.300 

346,300 

124,000 

93,000 

66,000 

96,000 

282,100 

95,400 

126,300 

195,400 

37,800 


21  15 

22  12 
21  02 
19  15 
19  35 
16  45 
15  45 

14  45 
12  52 
11  45 

21  15 

22  14 

23  27 
26  25 
33  30 
32  42 
26  30 
29  00 

15  20 
35  05 
39  55 
50  04 
48.56 
47  50 


2  60 

3  45 

0  25 

2  20 
5  20 

3  25 

1  00 
0  45 


2  01 
1  48 

3  00 


0  20 
126 
3  55 
0  32 

3  25 

4  35 

0  18 

1  30 
1  20 
153 


0  50 
4  35 
3  32 


1,416 
1,406 
1,418 
1,434 
1,431 
1,455 
1,462 
1,469 
1,481 
1,487 
1,416 
1,406 
1,394 
1,360 
1,267 
1,278 
1,359 
1,329 
1,465 
1,243 
1,165 
975 
998 
1,020 


9 

lO 

II 

12 

13 
14 
15 
i6 

17 
i8 
19 
20 
21 
22 

23 

24 


CHAP.   XXII. 


thl:  j!:AiiTjrs  axial  uotatwn. 


345 


RlVEUS 

FLOWING   TOWARDS 

THE  Equatou.     Eastern 

IlEillSPUEKE. 

Mouth  of  Riteb. 

Retabdation. 

II 

By  sediment 

By  water. 

Total 

Z>W.  if. 

F*tt  ptr 
etcond. 

Feet  per 
second. 

Footpoundt  per 
troond. 

Foot-poundt  ptr  steonit. 

Footpounds  per  teoond. 

I 

20  30 

1,423 

7 

527 

711,450 

711,977 

2 

21  16 

1,416 

10 

1,209 

1,632,150 

1,633,359 

3 

20  28 

1,423 

5 

403 

544,0.50 

544,4.53 

4 

18  20 

1,442 

8 

600 

810,000 

810,600 

5 

IG  50 

1,454 

23 

27,498 

37,122,300 

37,149,798 

6 

10  10 

1,459 

4 

656 

885,600 

886,256 

7 

L)  30 

1,464 

2 

13 

17,550 

17,563 

8 

14  35 

1,470 

1 

7 

9,450 

9,457 

9 

12  40 

1,482 

1 

9 

12,150 

12,159 

lO 

10  55 

1,492 

5 

244 

329,400 

329,644 

1 1 

21  10 

1,417 

1 

9 

12,150 

12,159 

12 

•21  48 

1,4]0 

4 

135 

182,250 

182,385 

13 

22  30 

1,403 

9 

943 

1,273,050 

1.273,993 

14 

24  52 

1,378 

18 

6,110 

8, 248,  {500 

S,2.j4,610 

15 

24  00 

1,388 

121 

5,140,969 

6,940,308,1.50 

6,945,449,119 

i6 

31  52 

1,290 

12 

6,975 

9,416,250 

9,423,225 

17 

25  15 

1,374 

15 

8,184 

11,048,400 

11,056,584 

i8 

27  50 

1,343 

14 

5,040 

6,816,150 

6,821,199 

•9 

13  50 

1.475 

10 

3,744 

5,054,400 

.5,058,144   1 

1 

20 

30  05 

1,314 

71 

5.')5,525 

749,958,750 

750,514,276   ' 

21 

39  52 

1,166 

1 

37 

49,950 

49,987 

22 

47  02 

1,035 

60 

177,609 

239,772,150 

239,949,759 

23 

47  06 

1,034 

39 

98,921 

133,.543,3.50 

133,642,271 

24 

46  50 

1,039 

19 

5,330 

7,19.5,500 

7,200,830 

346 


EADIANT  HEAT. 


CHAP.   XXII. 


KlVEItS   FLOWING    TOWARDS   THE    EqUATOU. 

Hemispheke. 


Eastern 


NAiiE  OF  River  or  District. 


River  Basin. 


Sq.  Miles. 


Deg.  M. 


East 

of 
outlet. 


West 

of 
outlet. 


«£ 


Volga 

Kuban 

Rioni 

Syrian  Mediterranean  rivers.. 

Jordan  district 

School! 

Axon  and  otliers 

Minder 

Sarabat 

Dnieper 

Bug  and  Indul 

Dneister 

Maritza 

Striman 

Vardar 

Drin 

Donau 

Tornea  and  Kcmi  district 

Wester  Botten 

Wester  Noniaud 

River  Dalil  district 

Clara  and  Gotlia  Elv 

Malar  district 

Eastern  part  of  South  Sweden 


557,700 

34,600 

17,900 

8,800 

12,400 

12,000 

23,600 

9,900 

8,300 

181,000 

27,400 

30,500 

23,700 

13,000 

12,300 

9,500 

293,100 

41,700 

36,900 

26,200 

20,300 

16,700 

9,400 

.5,800 


55  00 
44  50 
42  38 
33  40 
32  20 
47  40 
47  32 

47  40 

48  22 
5125 

49  05 
48  32 
42  00 
4128 

41  20 

42  10 
40  25 
67  20 
65  50 
63  30 
6116 
59  40 
59  45 

56  55 


0  10 


2  55 

0  50 

1  10 
0  35 

0  15 

2  00 

1  35 
1  15 


25 


45 


0  33 
121 
2  08 
0  22 
0  30 
010 

9  50 
0  05 
2  55 
158 
2  00 

110 
100 


871 

1,077 

1,118 

1,265 

1,285 

1,023 

1,026 

1,023 

1,009 

947 

905 

1,006 

1,129 

1,138 

1,141 

1,126 

1,047 

585 

622 

678 

730 

767 

765 

829 


14 
15 
i6 

17 
i8 

19 
20 
21 

22 

23 
24 


CHAP.   XXII. 


THE  EAirrirs  axial  hotatwn. 


347 


RiVEKS 

FLOWING    TOWARDS 

THE   EliDATOK.       ] 

]  ASTERN 

1Ii:misi'iiehk. 

Mouth  of  River. 

Retardation. 

4 
3 

^1 

By  sediment. 

By  water. 

Total 

j>ta.  if. 

Fttt  ptr 
mcond. 

Fest  per 
seootul. 

Foct-poundH  per 
tfcond. 

Foot-poundu  per  second. 

Fooi-pound» per  second. 

I 

46  10. 

1,052 

181 

7,137,020 

9,634,085,100 

9,642,122,120 

2 

44  42 

1,080 

3 

121 

163,350 

103,471 

3 

42  15 

1,124 

6 

251 

338,850 

339,101 

4     38  22 

1,268 

3 

30 

40,500 

40,530 

5     31  48 

1,290 

6 

121 

163,350 

103,471 

6     46  45 

1,041 

18 

1,518 

2,049,300 

2,050,818 

7     46  40 

1,042 

16 

2,360 

3,180,000 

3,188,360 

8     47  30 

1,026 

3 

35 

47,250 

47,285 

9  !  48  18 

1,010 

1 

3 

4,050 

4,053 

lO     46  40 

1.042 

95 

638,115 

801,4.5,5,250 

862,093,365 

11      46  42 

1,042 

47 

23,646 

31,922,100 

31,94.%740 

12     46  20 

1,049 

43 

22,029 

29,739,1.50 

29,761,179 

13  '  40  4i5 

1,148 

19 

3,342 

4,511,700 

4,51.5,042 

14  '  40  55 

1,148 

10 

507 

684,4.50 

684,957 

15  1  40  32 

1,154 

13 

812 

1,090,200 

1,097,012 

16     41  40 

1,135 

9 

302 

407,700 

408,002 

17     45  15 

1,069 

22 

55,396 

74,784,000 

74,839,996 

18  1  65  52 

621 

36 

21,111 

28,499,850 

28,-520,961 

19  i  64  40 

650 

28 

11,301 

15,256,3.50 

15,267,651 

20  ]  62  20 

705 

27 

7,460 

10,071,000 

10,078,460 

21      60  35 

750 

20 

3,172 

4,282,200 

4,285,372 

22     D7  48 

809 

42 

11,506 

15,533,100 

1.5,  .544, 606 

23  '  50  25 

773 

8 

235 

317,2.^0 

317,485 

24 

1  56  15 

844 

15 

510 

'             688,  .500 

689,010 

348 


EABIANT  HEAT. 


CHAP.  XXII. 


klvers  plowing  towards  the  equator.     eastern 
Hemisphere. 


Name  op  Riveb  or  District. 


River  Basin. 


Sq.  Miles. 


5°  g 
3       " 


East 

of 
outlet. 


Deg.  M. 


West 

of 
outlet. 


Western  part  of  South  Sweden. 
Glommen  and  Lauven  district.. 

Southern  part  of  Norway 

E.  coast  of  Adriatic 

Grulf  of  Taranto  and  Ionian  Sea. 
Western  part  of  South  Italy. . . 

Tiber 

Arno  and  W.  coast  Central  Italy 

Etsch  district 

Po 

Rhone 

Ter  and  Slobregat 

Ebro 

Guadalaviar 

Jucar 

Segura  

Guadalquiver 

Gnadiana 

Caldoa 

Tflgus 

Duero 

Minho 

Rivers  of  Great  Britain 

Rivers  of  Ireland 


6,600 

21,300 

9,500 

17,200 

7,500 

11,900 

7,200 

8,900 

12,000 

28,100 

38,000 

11,200 

33,200 

8,900 

8,100 

8,200 

20,000 

25,700 

7,100 

28,900 

38,700 

10,600 

46,015 

16,224 


57  30 
60  52 
59  18 
43  50 

40  00 

41  15 

42  42 

43  25 
46  15 
45  25 
45  42 
42  45 
42  06 
40  10 

39  15 
38  10 

37  40 

38  25 
37  48 

40  00 

41  30 

42  41 


0  42 


0  20 

0  30 
0  17 
0  32 


0  41 


2  02 

2  00 
0  20 

3  50 
3  05 
115 


0  04 
0  15 

0  25 


0  34 
3  10 

0  25 
2  20 

0  54 
115 

1  20 


817 
740 
776 
1,096 
1,164 
1,142 
1,116 
1,103 
1,050 
1,065 
1,061 
1,115 
1,127 
1.161 
1,176 
1,194 
1,202 
1,190 
1,200 
1,164 
1,139 
1,117 


'3 
14 

f5 
i6 

'7 
[8 

'9 

20 


CHAP.  XXII. 


THE  EAETWS  AXIAL  llOTATION. 


349 


lllVEItS 

I'LOWING   TOWARDS 

THE  Equator.    Eastern 

Hemisphere. 

Mouth  of  Riyeb. 

Retabdatiox.                                I 

0 

3 

By  sediment. 

By  water. 

Total 

/>«».  j^. 

Ftttper 
ttcond. 

Feet  per 
itecoiui. 

Foot-pounds  per 
tteond. 

Font-pounde  per  second. 

Foot-pounds  per  eeeond. 

I 

56  40 

835 

18 

835 

1,127,250 

1,128,085 

2 

50  10 

779 

39 

12,658 

17,088,300 

17,100,958 

3 

58  10 

801 

26 

2,320 

3,132,000 

3,134.320 

4 

43  30 

1,102 

6 

241 

325,350 

325,591 

5 

39  30 

1,172 

8 

188 

253,800 

253,988 

6 

40  40 

1,152 

10 

407 

630,450 

630,017 

7 

41  45 

1,133 

17 

814 

1,008,900 

1,000,714 

8 

43  00 

1,111 

8 

223 

301,050 

301,273 

9 

45  00 

1,074 

24 

2,700 

3,045,000 

3,647,700 

lO 

44  50 

1,077 

12 

1,412 

1,906,200 

1,907,612 

11 

43  25 

1,103 

42 

26,182 

35,345,700 

35,371,882 

12 

42  40 

1,117 

2 

18 

24,300 

24,318 

13 

41  02 

1,146 

10 

4,681 

6,319,350 

6,324,031 

14 

39  20 

1,175 

14 

681 

010,350 

920,031 

>5 

39  00 

1,180 

4 

51 

08,850 

68,901 

i6 

38  06 

1,195 

1 

3 

4,050 

4,053 

17 

36  42 

1,218 

16 

2,000 

2,700,000 

2,702,000 

i8 

36  48 

1,216 

26 

6,785 

9,159,750 

9,166,535 

19 

37  40 

1,202 

2 

11 

14,850 

14,861    1 

20 

38  60 

1,183 

19 

4,075 

5,501,250 

5,505,325 

21     41  15 

1,142 

3 

135 

182,250 

182,385 

22     42  28 

1,121 

4 

66 

80,100 

80,106 

23 

1,181 

1,594,350 

1,505,  .531 

24 

021 

1,243,350 

1,244,271 

350 


RADIANT  HEAT. 


CHAP.   XXII. 


RiVEKS   FLOWIXG    TOWARDS   THE    EQUATOR.       AVeSTERN 

Hemisphere. 


Naste  of  River  or  District. 


RivEE  Basin. 


Sg.  Mltu. 


Deg.  M. 


East 

of 

outlet. 


West 

of 
outlet. 


Deg.  M 


Bastard,  Pentecost 

Sagueiiay 

St.  John,  Penobscot 

Kennebec,  Androscoggin,  Saco 

Merrimack 

Connecticut 

Hudson,  Housatonic 

Delaware 

Susquelianna 

Potomac,  Rappahannoclv 

.James 

Roanoke,  Tar 

Santee,  Neuse 

Savannah  and  others 

Alabama  district 

Mississippi 

Colorado,  Brazos,  'J'rinidad  . . 

Rio  del  Norte 

Colorado 

E.  coast  Gulf  of  California. . . 


33,000 

27,800 

34,400 

13,000 

7,100 

10,800 

16,000 

11,500 

27,200 

16,000 

13,100 

18,800 

44,100 

,^1,200 

128,700 

,244,000 

191,200 

-2V:^SM){) 

267,000 

140,000 


50  50 
49  02 
46  40 
44  45 
43  20 
43  20 
42  30 
41  00 
41  14 
89  00 
37  32 
36  36 
34  40 
32  51 
31  30 
40  55 
31  12 
29  50 
36  04 
28  06 


0  02 
0  04 
0  03 


0  25 


1  06 
1  10 


0  05 
2  45 

1  00 
0  20 
0  38 


0  52 

1  15 
1  32 
1  40 
1  25 
1  05 

7  10 
1  .50 
6  40 


959 
996 
1,042 
1,078 
1,105 
1,105 
1,120 
1,146 
1,142 
1,180 
1,204 
1.220 
1,249 
1,276 
1,295 
1,148 
1,300 
1,318 
1,228 
1,340 


CHAP.  XXII. 


THE  KARTWa  AXIAL  ROTATION. 


351 


ItlVElis    FLUWINO    TOWARDS 

1 

TlIK    EcjU.VTOU.       WeSTEBN 

Hemispuekh. 

Mouth  of  Riveb. 

Rktaedahon. 

•3 
1 

s  1 

By  sediment. 

By  water. 

Total. 

7)^.   .v. 

Fttt  per 
tecond. 

Faet  per 

»tCOHd, 

Foot-poundt  per 
ercottd. 

Fool-pounde  per  teeond. 

Foot-pounds  per  ueond. 

I 

49  08 

994 

35 

15,790 

21,316,500 

21,332,290 

2 

48  00 

1,017 

21 

4,788 

6,463,800 

6,468,588 

3 

45  20 

1,068 

26 

9,081 

12,259,8.50 

12,268,431 

4 

43  55 

1,094 

16 

1,300 

1,755,000 

1,756,300 

5 

42  48 

1,114 

9 

225 

303,750 

303,975 

6 

41  10 

1,143 

38 

6,091 

8,222,850 

8.228,941 

7 

40  42 

1,152 

32 

6,400 

8,640,000 

8,646,400 

8 

39  35 

1,172 

26 

3,036 

4,098,600 

4,101,636 

9 

39  32 

1,172       30 

9,561 

12.907,350 

12,916,911 

lO 

38  02 

1,197  '     17 

1,806 

2,488,100 

2,439,906 

1 1 

36  52 

1,215 

11 

619 

835,6.50 

836,269 

12 

35  52 

1,221 

11 

888 

1.198,800 

1,199,688 

'3 

33  42 

1,264 

15 

3,881 

5,239,350 

5,248.231 

'4 

31  52 

1,290 

14 

3,917 

5,287,950 

5.291.867 

•5 

30  15 

1,312 

17 

14,  .543 

19,633,0.50 

19,647.-593 

i6 

29  08 

1,327 

179 

14,323,668 

19,336,951,800 

19,351,275,468 

17 

28  40 

1,333 

33 

81,354 

109,827,900 

109,909,254 

i8 

25  30 

1.371 

53 

236,457 

319,216,950 

319,453,407 

•9 

32  15 

1.285 

57 

338,890 

457,501,500 

457,840,390 

20 

27  00 

1,353       13 

9,240 

12,474,000 

12.483,240 

352 


RADIANT  HEAT. 


CHAP.   XXII. 


ElVEi;S   FLOWING   TOWARDS   THE    EQUATOR.       WeSTEKX 

Hemisphere. 


Najie  of  Utter  or  Disteict. 


■RiTER  Basin. 


Sq.  itiles. 


Deo-  J/. 


East 

of 
outlet. 


Dea.  M. 


West 
of 

outlet. 


Kalamatli  and  Tsashtl 

Columbia 

Frazer 

Simpson  and  Frances  district. 

Atna  or  Copper 

Bolsas,  Yopez,  Verde 

Sirano  district 

San  Juan  de  Mcaragua. . . . 

Sacramento 

Paraliyba  and  Grande 

Ciara,  Croayhn 

Jaguaribe 

Belmoute  and  Doce  dist.. . . 

Paraliyba   (Sontli) 

San  Francisco 

Paranahyba 

Maranhao  and  Itaqieura. . . 

Gurupy  and  Turyassu 

Tocantins 

Amazon 


42,900 

283,400 

138,300 

53,600 

34,900 

71,. 500 

24,700 

23,700 

33,000 

37,600 

33,700 

19,900 

114,400 

35,800 

247,600 

157,300 

59,600 

49,000 

376,000 

2,236,000 


42  00 

45  52 

5128 

56  40 

62  12 

18  00 

14  00 

12  00 

40  00 

6  40 

5  08 

5  50 

17  25 

22  00 

14  00 

8  05 

5  00 
3  20 

10  10 

6  20 


1  15 

7  02 

2  00 
0  05 
0  05 
0  10 


0  40 


1  20 

0  08 

1  50 
0  05 

0  30 

1  48 

2  12 
7  00 
2  30 

0  40 
100 

1  00 
1250 


1,129 
1,058 
946 
835 
708 
1,445 
1,474 
1,486 
1,164 
1,509 
1,513 
1,511 
1,449 
1,408 
1,475 
1,504 
1,513 
1,516 
1,495 
1,510 


/ 
8 

9 

lO 

II 

12 

'3 
14 
IS 
i6 

17 
i8 

19 
20 


CHAP.   XXII. 


THE  EARTH'S  AXIAL  ROTATION. 


353 


KlVERS 

PLOWING  TOWARDS  TUE  EqDATOR.      WeSTERK 

Hemisphere. 

Mouth  of  Riveb. 

Retakdation. 

1 

3 

II 

i    -S" 

By  sediment. 

By  water. 

Total. 

D«(7.  JA. 

Fe«t  per 
tecowL. 

Fat  per 
second. 

Foot-pounds  par 
gecond. 

Fool-pound »  per  aecorui. 

Foot-pounds  per  second. 

I 

41  45 

1,133 

4 

268 

361,800 

362,068 

2 

45  48 

1,059 

1 

111 

149,850 

149,961 

3 

49  02 

996 

50 

135,050 

182,317,500 

182,452,650 

4 

55  10 

871 

36 

27,135 

36,632,250 

36,659,385 

5 

60  20 

752 

44 

26,393 

35,630,550 

35,656,943 

6 

16  42 

1,455 

10 

2,788 

3,763,800 

3,766,588 

7 

13  30 

-1,477 

3 

86 

116,100 

116,186 

8 

11  15 

1,490 

4 

148 

199,800 

199,948 

9 

37  50 

1,200 

36 

16,706 

22,553,100 

22,569,806 

lO 

5  40 

1,512 

3 

132 

178,200 

178,332 

1 1 

3  10 

1,517 

4 

211 

284,850 

285,061 

12 

4  30 

1,514 

3 

70 

94,500 

94,570 

J3 

17  00 

1,453 

4 

715 

965,250 

965,965 

H 

21  30 

1,413 

5 

349 

417,150 

417.499 

'5 

10  SO 

1,494 

19 

34,912 

47,131,200 

47,166,112 

i6 

2  58 

1,517 

13 

10,382 

14,015,700 

14,026,082 

17 

2  50 

1,517 

4 

373 

503,520 

503,893 

i8 

1  00 

1,519 

3 

172 

232,200 

232,372 

19 

2  00 

1,518 

23 

77,738 

104,946,200 

105,023,938 

20 

1  25  < 

1,519 

9 

70,993 

95,840,550 

95,911,543 

354  BADIANT  HEAT.  chap.  xxii. 

The  last  column  of  the  preceding  tables  contains  the 
amount  of  retardation  caused  by  the  waters  of  rivers  flowing 
towards  the  equator.  The  computation  of  the  retarding 
energy  being  based  on  the  Aveight  of  water  discharged  and 
the  increase  of  rotary  velocity  acquired  during  the  transfer 
from  the  source  to  the  outlet,  no  question  can  be  raised  as 
to  the  existence  of  the  retardation  entered  in  the  tables  ;  but 
Avhether  compensating  energies  are  called  forth  by  the  I'eturn- 
ing  vapors  before  the  condensation  takes  place  which  results 
in  the  precipitation  on  the  river  basins,  demands  careful 
consideration.  Dr.  Mayer,  in  his  discourse  previously  ad- 
verted to,  positively  asserts  that,  agreeably  to  the  demonstra- 
tion of  Laplace,  based  on  abstract  mechanical  principles,  the 
compensating  energy  corresponds  in  every  instance  with  the 
amount  of  retardation  to  which  the  rotaiy  motion  of  the' 
globe  may  be  subjected.  Admitting  this  conclusion  to  be 
correct,  Ave  must  assume  the  adequacy  of  the  vapojs  Avhich 
rise  within  the  tropics  to  restore,  during  theii"  transfer  to 
the  temperate  and  polar  regions,  the  loss  of  ?'/s  viva  occa- 
sioned by  the  condensed  Avater  Avhich,  in  the  form  of  rivers, 
flows  towards  the  equator.  ObA'iously,  such  restoration  of 
energy  could  only  be  effected  by  friction  or  pressure  of  the 
vapors  against  projections  on  the  earth's  surface  directly,  t)i' 
through  the  interA^ention  of  particles  of  the  atmospheric  air 
put  in  motion  by  the  A^apors.  The  Astronomer-Eoyal  of 
Sweden,  in  an  elaborate  demonstration  presented  to  the 
Eoyal  Academy  of  Sciences  at  Stockholm,  in  refutation  of 
my  assertion  that  solar  influence   is    capable    of  diminishing 


CHAP.  XXII.  THE  EAETWH  AXIAL  liOTATION.  365 

perceptibly  the  rotary  velocity  of  the  earth,  thus  states  the 
case:  "The  globe  aud  its  atmosphere  constitute  a  combiuecl 
system  iu  luotiou,  iu  which  no  part  can  by  any  outside  cause 
be  disturbed  in  its  relative  position  without  the  motion  of 
the  entire  system  being  thereby  influenced.  Consequently,  a 
body  of  air  which,  for  instance,  is  carried  from  the  direc- 
tion of  the  equator  towards  either  of  the  poles  must,  by 
degrees,  positively  part  with  the  excess  of  rotary  vis  viva 
which  it  possessed  at  the  commencement  of  the  motion, 
compared  with  the  rotary  velocity  of  the  region  to  which 
it  has  been  transferred,  and  must  impart  the  entire  surplus 
to  the  earth  undiminished,  the  rotation  of  which  must  con- 
sequently ha  accelerated  by  this  current  of  air ;  and,  con- 
versely, a  current  of  air  of  contrary  direction,  or  from  either 
of  the  poles  towards  the  equator,  must  produce  retardation. 
No  dilierence  can  exist  iu  this  respect  between  a  curi'ent  of 
water  aud  a  carrent  of  air."  The  Swedish  astronomer,  like 
Laplace,  thus  puts  the  \vhole  question  in  a  nutshell,  assert- 
ing that  air  and  water,  water  and  air,  may  circulate  in  any 
manner  whatever  between  the  equator  and  the  poles,  aud 
between  the  poles  and  the  equator,  without  influencing  the 
axial  rotation  of  the  globe.  It  is  very  true  that  the  earth, 
with  its  rivers  aud  atmosphere,  constitute  a  "  combined  sys- 
tem in  nidtion";  but  we  must  not  lose  sight  of  the  import- 
ant fact  that  an  outside  energy — the  sun's  radiant  heat — is 
being  continually  exerted,  A\liich  interferes  Avith  the  motions 
within  that  combined  system.  Accordingly,  no  argument 
can    prove    the   correctness  of   the  statement  laid  before  the 


356  RADIANT  MEAT. 


CHAP.  XXII. 


Royal  Academy  of  Sciences  at  Stockholm  short  of  a  posi- 
tive demoustratiou  showing  that  particles  of  vapor  corre- 
sponding in  weight  with  the  water  dischargeil  by  some 
river — say  the  Mississi^jpi — are  capable  of  imparting  by 
friction  against  the  earth's  surface,  directly  or  through  the 
agency  of  the  atmosphere,  a  rotary  force  exactly  balancing 
the  retarding  energy  which  we  have  established. 

The  advocates  of  the  theory  of  compensation,  \vhile  ad- 
mitting that  they  cannot  furnish  any  'practical  evidence  of 
the  truth  of  their  doctrine,  assert  that  the  subject  is  not 
susceptible  of  experimental  test.  It  would,  indeed,  be  a 
fruitless  task  to  undertake  the  construction  of  anemometers, 
or  similar  instruments,  showing  that  the  pressure  and  friction 
of  the  particles  of  the  retui'ning  vapor,  exerted  directly  or 
through  atmospheric  intervention  against  the  surface  of  the 
Mississip25i  river  basin,  from  west  to  east,  are  capable  of  com- 
pensating the  established  retardation  of  19,336,000,000  foot- 
pounds per  second. 

The  admitted  impossibility  of  proving  by  direct  measure- 
ment the  existence  of  compensating  force  has  suggested  the 
resort  to  some  indirect  method.  I  have  accordingly  con- 
structed an  instrument  which  practically  demonstrates  the 
truth  of  the  following  proposition,  on  which  the  solution  of 
the  problem  unquestionably  depends :  The  retarding  influ- 
ence produced  by  currents  of  water,  confined  wdthin  channels 
which  convey  a  given  weight  in  a  given  time,  from  the  pole 
to  the  equator  of  a  rotating  sphere,  cannot  be  compensated 
by  ojjposite  currents  of  vapor  transferring  an  equal  weight 


CHAP.  XXII.  THE  EARTH'S  AXIAL  liOTATlOX.  357 

in   equal   time   over  the  surface   of  tbe   f^aid   sphere  from  its 
equator  to  its  pole. 

The  illustration  on  Plate  34  represents  the  instrument 
adverted  to;  but  before  entering  on  a  description,  it  -will  be 
well  to  define  clearly  the  problem  intended  to  be  solved  by 
experimental  demonstration.  The  rotary  velocity  of  the  sur- 
face of  the  eai-th,  for  instance,  on  the  45th  parallel  is  1,074 
ft.  per  second,  that  of  the  equator  1,519  ft.  per  second ; 
hence  the  water  of  a  river  flowing  from  lat.  45  deg.  to  the 
equator  will  have  its  velocity  round  the  axis  of  the  earth 
increased  1,519  —  1,074  =  445  ft.  per  second.  It  needs  no 
demonstration  to  sbow  that  the  expenditure  of  energy  neces- 
sary to  produce  tliis  increase  of  rotaiy  velocity  will  cause 
the  earth  to  rotate  at  a  diminished  rate ;  the  amount  of 
retarding  force  being  readily  ascertained  by  multiplying  the 
weight  of  water  transferred  by  the  height  necessary  to  gene- 
rate a  velocity  of  445  ft.  per  second,  viz.,  3,094  ft.  Conse- 
quently, each  pound  of  water  transferred  from  lat.  45  deg. 
to  the  equator  demands  the  expenditure  of  a  dynamic  enei'gy 
of  3,094  foot-pounds.  The  question  now  presents  itself, 
Avhether  a  pound  of  water  evaporated  on  the  equator,  and 
returned  in  the  form  of  vapor  to  lat.  45  deg.,  can,  during 
the  return  movement,  impart  a  rotary  energy  of  3,094  foot- 
pounds to  the  earth.  Of  coui-se  the  vapor,  on  leaving  the 
equator,  possesses  a  rotary  velocity  of  1,519  ft.  per  second, 
while  the  sui-face  of  the  earth  in  lat.  45  deg.  rotates,  as  be- 
fore stated,  at  a  rate  of  only  1,074  ft.  per  second.  It  will 
be  evident,  therefore,   that   during  the  return  movement  the 


358  RADIANT  HEAT.  chap.  xxir. 

vapor,  by  contact  with,  the  eai'tli,  will  have  its  rotary  velocity 
diminished  in  the  ratio  of  1,519  :  1,074.  On  purely  theo- 
retical considerations,  it  must  be  admitted  that  this  contact, 
1)}'  ^vhich  the  returning  pound  of  vapor  has  its  rotary  velo- 
city diminished  445  ft.  per  second,  will  restore  to  the  earth 
the  whole  of  the  energy  which  was  previously  expended  in 
augmenting  the  speed  of  the  pound  of  water  fi'om  1,074  to 
1,519  ft.  per  second  during  its  transfer  from  lat.  45  deg.  to 
the  equator.  But  practice  shows  that  rotary  motion  cannot 
be  imparted  to  cylindrical  or  spherical  bodies,  however 
rough  their  surface  may  be,  by  currents  of  air  or  steam,  with- 
out great  loss  of  mechanical  energy.  Conversely,  currents 
of  air  or  steam  cannot  be  produced  by  the  action  of  similar 
rotating  bodies  Avithout  a  corresponding  loss  of  mechanical 
energy. 

Practical  engineers  familiar  with  these  facts  fully  appre- 
ciate the  difficulty  of  instituting  experiments  intended  to 
determine  exactly  what  amount  of  force  is  expended  in  caus- 
ing rotary  motion  by  currents,  and  what  amount  of  force  is 
developed  hj  cui-rents  produced  by  rotating  bodies,  as  sup- 
posed. The  illustrated  dynamic  register,  Plate  34,  obviates 
this  difficult  comparison  between  energy  expended  and  de- 
veloped, by  the  simple  expedient  of  applying  heat  and  cold 
in  such  a  manner  that  the  retarding  influence  of  a  current 
of  water  flowing  from  the  pole  to  the  equator  acts  simul- 
taneously with  the  accelerating  influence  of  an  opposite 
current  of  vapor,  transferring  equal  Aveight  in  equal  time, 
from  the   equator   towards  the  pole.     The   detail   of   the  in- 


CHAP.  XXII.  THE  EAIiTirS  AXIAL  nOTATWN.  359 

stiumeut  will  be  understood  by  the  following  description : 
Fig.  I.  slioAvs  a  section  of  a  hollow  sphere  6.25  ins.  dia- 
meter, composed  of  very  thin  brass  partially  filled  Avith  a 
light  non-conducting  substance,  made  to  revolve  on  its  ver- 
tical axis ;  the  upper  half  being  covered  with  a  light  semi- 
spherical  casing,  extending  a  short  distance  below  the  hori- 
zontal central  plane  of  the  sphere.  A  cylindrical  cistern, 
provided  with  a  flat  cover,  is  attached  to  the  top  of  the 
semi-spherical  casing.  The  mode  of  supporting  the  lower 
pivot  on  which  the  sphere  turns,  as  also  the  axle  at  the  top, 
Avill  be  seen  by  reference  to  the  drawing.  Rotary  motion 
is  imparted  to  the  sphere  by  a  horizontal  toothed  rack  (see 
top  view.  Fig.  II.)  working  into  the  teeth  of  a  wheel  at- 
tached to  the  vertical  axle;  the  moti^■e  power  consisting  of 
a  weight  suspended  by  a  light  cord  passing  over  a  pulley 
and  secured  to  the  rack.  A  circular  gas-pipe,  provided  with 
a  series  of  burners,  surrounds  the  sphere  some  distance  be- 
low its  centre.  Referring  to  Fig.  II.,  it  will  be  seen  that 
the  guide-pieces  which  support  the  horizontal  rack,  and 
through  which  it  slides,  act  as  stops  which  regulate  the  ex- 
tent of  the  movement.  It  should  be  particularly  noticed 
that  the  arrangement  is  such  that  when  the  motion  is 
checked  by  the  -  right-hand  stop  the  last  cog  of  the  rack 
has  just  slipped  out  of  the  cog-wheel,  thus  allowing  the 
sphere  to  turn  freely.  The  extent  of  motion  of  the  rack  is 
O.lJ^G  ft.,  and  the  weight  exactly  2  lbs.  It  mil  be  seen, 
therefore,  that  the  motive  force  is  0.1 8G  X  2  =  0.372  foot- 
pound, or  2    X    7,000   X  0.18G  =  2,604  foot-grains.     Deduct- 


360  RADIANT  HEAT.  chap.  xxii. 

ing  the  loss  by  friction — 64  foot-gi'ains- — tlie  effective  motive 
power  will  be  2,540  foot-grains.  The  axis  of  the  sphere 
being  exactly  vertical,  there  is  obviously  no  friction  what- 
ever at  the  tipper  bearing  after  the  slipping  of  the  last  cog 
of  the  rack,  while  the  lower  pivot  presents  a  mere  point 
of  hardened  steel  to  the  step  under  it;  hence  the  over- 
coming the  atmospheric  resistance  against  the  outside  of  the 
sphere  and  the  cistern  may  be  considered  as  the  only  work 
to  be  performed  by  the  stated  available  motive  power  of 
2,540  foot-grains.  It  only  remains  to  be  noticed  that  when 
the  sphere  is  to  be  put  in  motion  the  rack  is  geared  into 
the  cog-wheel  and  brought  up  against  the  left-hand  stoj),  as 
represented  in  the  drawing,  the  check-lever  (Fig.  IV.)  being 
at  the  same  time  placed  in  the  position  shown  by  the 
dotted  lines.  The  moment  for  starting,  indicated  by  the 
chronometer,  having  ariived,  the  check-lever  is  brought  to 
the  horiiiontal  position  as  quickly  as  possible,  in  order  to 
prevent  di'agging  at  the  moment  of  lil^erating  the  toothed 
rack.  As  shown  by  the  illustration,  a  small  quantity  of 
water  is  confined  within  the  surrounding  casing  of  the 
sphere,  thus  forming  an  aqueous  belt  round  its  equator ; 
the  polar  cistern  being  filled  with  water. 

The  object  of  the  instrument  having  been  clearly  set 
forth,  it  scarcely  needs  explanation  that  the  device  is  in- 
tended to  show  that  when  the  heat  of  the  gas-flames  is 
applied  to  the  aqueous  belt,  causing  evaporation,  while  con- 
densation is  effected  by  the  cold  water  in  the  polar  cistern, 
the  motive  energy   (2,540  foot-grains)   will   be    incapable  of 


CUAI'.  XXII.  THE  EAETWS  AXIAL  BOTATION.  3C1 

turulug  the  sphere  as  fast  aud  as  long  as  when  heat  and 
refiigeratiou  are  not  applied.  This  assumption,  it  will  be 
perceived,  is  in  direct  opposition  to  the  views  held  l)y  the 
Asti'onomer  Royal  at  Stockholm  and  other  followers  of  La- 
place, who  contend  that  "no  difference  can  exist"  as  regards 
the  effect  on  the  axial  rotation  of  the  globe  between  currents 
of  water  and  currents  of  aeriform  matter  transferring  equal 
Meight  in  equal  time. 

The  mode  of  conducting  the  experiment  with  the  dynamic 
register  will  be  readily  undei-stood  b}'  the  following  explana- 
tion: The  polar  cistern  is  charged  \\\i\i  boiling  water,  and 
the  gas-flames  applied  for  a  fe^v  minutes  until  the  water 
round  the  equator  is  brought  near  boiling  heat.  The  gas  is 
then  shut  off,  and  the  toothed  rack  geared  aud  afterwards 
locked  by  the  check-lever.  The  chronometer  being  then 
carefully  observed,  the  check-lever  should  be  quickly  pushed 
down  when  the  hand  marks  exact  time.  The  motive  weight, 
being  thus  liberated,  puts  the  sphere  in  moticm  through  the 
inteiTention  of  the  rack  and  cog-wheel,  the  time  elapsing 
between  the  commencement  of  the  movement  and  the  slip- 
ping of  the  last  tooth  of  the  rack  occupying  about  one 
second.  The  observation  of  the  chronometer  should  con- 
tinue, in  order  to  ascertain  the  exact  time  when  the  sphei'e 
is  brought  to  rest.  In  the  meantime,  the  number  of  turns 
must  be  accurately  coiinted.  The  fii'st  experiment  being  con- 
cluded, the  sphere  is  again  put  in  motion,  as  before,  without 
changing  the  water  in  the  polar  cistern  or  applying  the  gas- 
flames,  the   object   of   employing   heat   before  starting  being 


362  EABIANT  HEAT.  chap.  xxii. 

merely  that  of  expaudliig  the  sjahere  to  proper  dimensions. 
The  experiment  having  been  repeated  six  times,  the  'Dieuji 
of  time  occupied  and  number  of  turns  performed,  resulting 
from  the  expended  energy  of  2,540  foot-graius,  should  be 
determined  ^vith  the  utmost  precision.  The  procedure  will 
then  be  changed  :  the  polar  cistern  ^vill  be  charged  with 
cold  water,  and  the  gas-ilames  applied  and  kept  burning. 
The  sphere,  under  these  altered  conditions,  is  again  started, 
but  not  until  boiling  temperature  in  the  equatorial  belt  has 
been  attained  and  evaporation  commenced.  The  experiment, 
as  before,  will  be  repeated  six  times,  and  the  mean  of  time 
and  the  number  of  turns  ascertained. 

The  law  of  compensation  relating  to  solar  influence  on 
the  axial  rotation  of  the  earth,  expounded  by  Dr.  Mayer, 
is  evidently  strictly  applicable  to  the  dynainic  register,  since 
the  equatorial  belt  of  the  rotating  sphere  is  being  continu- 
ally heated,  while  the  polar  region  is  being  exposed  to  con- 
tinuous refrigeration,  vapor  being  thus  foi'med  at  the  equator, 
and  currents  produced  which  condense  on  reaching  the  cold 
semi-sj^herieal  covering  over  the  pole.  The  water  thus 
formed,  divided  into  small  sti'eams,  flows  back  on  the  sur- 
face of  the  sphere  to  the  equator,  where  it  is  again  converted 
into  vapor;  hence  a  continued  circiilation  of  opposite  cur- 
rents of  vapor  and  water  wall  be  kept  up.  It  sliould  be 
particularly  observed  that  the  vapor  in  its  passage  toAvards 
the  pole  not  only  acts  against  the  sxirface  of  the  sphere, 
but  also  against  the  inside  of  the  semi-spherical  covering, 
thereby  affording  a  double   chance   of    imparting    motion    to 


CHAP.  XXI f.  THE  EAETWS  AXIAL  ROTATION.  363 

the  rotating  mass.  But  this  notwithstanding,  the  exjieri- 
meuts  have  .shown  tliat  the  retanlimj  energy  of  the  con- 
densed water  flowing  in  small  streams  from  the  jwle  to  the 
equator  on  tlie  surface  of  the  sphere,  greatly  exceeds  the 
accelerating  energy  imparted  by  the  excess  of  rotary  velocity 
of  the  vapor  in  its  course  towards  the  pole,  and  the  conse- 
quent friction  of  its  particles  against  the  sui-faces  of  the 
sphere  and  the  semi-spherical  casing.  Agreeably  to  Dr. 
Mayer's  conclusion.s,  founded  on  the  theory  of  Laplace,  the 
opposite  currents  which  result  from  high  temperature  on 
the  equator,  and  the  refrigeration  over  the  temperate  zone 
and  the  poles,  cannot  affect  the  axial  rotation  of  the  globe. 
"  The  effect  of  every  single  motion  by  these  means  on  the 
rotation  of  the  globe,"  he  saj-s,  "is  exactly  compensated  by 
the  effect  of  another  motion  in  an  opposite  direction."  Nor 
can  the  Swedish  Astronomer,  as  we  have  seen,  perceive  any 
difference  between  currents  of  water  and  currents  of  ai-ri- 
form  matter.  In  direct  opposition  to  the  conclusions  of  these 
physicists,  our  expeiiments  prove  that,  although  the  weight 
transferred  fi-om  the  pole  to  the  equator  of  the  sphere  of 
the  dynamic  register  is  precisely  the  same  as  the  weight 
which  is  transferred  in  the  oi)posite  direction,  the  contact 
and  friction  of  the  particles  of  vapor  against  the  surfaces  of 
the  convex  and  concave  spheres  is  incapable  of  restoring  the 
loss  of  vis  viva  consequent  on  imparting  rotary  motion  to 
the  particles  of  water  transferred  fi"om  the  pole  to  the 
equator. 

Too   much   space   would   be   occupied   by   a   detailed  ac- 


364-  BABIANT  HEAT.  CHAP.  xxii. 

count  of  the  experiments  whicli  Lave  been  made  with  the 
dynamic  register;  hence  only  the  most  important  facts  bear- 
ing directly  on  the  question  will  be  presented.  The  number 
of  turns  of  the  rotating  sphere  produced  by  the  nioti\-e 
force  of  2,540  foot-grains  has  been  660.5,  ocoup3ing  10  inin. 
37  sec,  the  barometer  at  the  time  indicating  29.8,  the  tem- 
perature of  the  surrounding  atmosphere  being  62°  F.  The 
mean    of   the   force    expended   for    each  turn   will   therefore 

2,540 
amount    to  — -7—  =  3.84   foot-grains.      It   will    be   asked,    in 
060.5 

view  of  this  insignificant  motive  power,  chiefly  expended 
in  overcoming  the  atmospheric  resistance  against  the  rotat- 
ing sphere  and  cistern,  how  the  excess  of  retarding  energy 
of  the  condensed  water  flowing  over  the  surface  of  the 
sphere,  from  the  pole  to  the  equator,  can  possibly  be  mea- 
sured. The  answer  is  that  we  need  not  consider  the  amount 
of  energy  developed  by  the  motive  Aveight ;  we  merely  count 
the  number  of  turns  and  note  the  time  required  to  bring 
the  sphere  to  a  state  of  rest  from  the  moment  of  stai'ting, 
the  gas-flames  being  kept  burning  and  the  refrigerating 
medium  retained  in  the  polar  cistern  during  the  observations. 
Then,  removing  the  cooling  medium  and  replacing  the  same 
with  boiling  water,  we  again  put  the  sphere  iu  motion,  count 
the  number  of  turns,  and  note  the  time.  The  result  of  this 
change  of  procedure  will  be,  as  shown  l^y  our  experiments, 
that  the  sphere  will  run  much  longer  and  perform  a  greater 
number  of  turns — a  startling  fact,  since  the  motive  energy 
of  2,540   foot-grains    has    not  been    increased.     To   practical 


CHAP.  SXii.  TEE  ICAHTn'S  AXIAL  liOTATION.  366 

minds  the  explanation  will  at  once  suggest  itself,  that 
because  there  is  an  expenditure  of  lient  while  condensation  is 
kept  up,  which  ceases  when  the  refrigerating  medium  is 
withdrawn,  some  additional  work  is  being  performed  Avhile 
the  cold  medium  I'emains  at  the  pole.  Now,  what  is  the 
nature  of  this  Avork  ?  Evidently  the  condensed  water,  while 
flowing  from  the  pole  to  the  equator,  has  its  rotary  speed 
successively  increased  corresptmding  with  that  of  the  sur- 
face of  the  sphere ;  hence  work  must  be  performed  ^vhi]e 
refrigeration  is  kept  up  at  the  pole.  Satisfactory  as  this 
explanation  appeai-s,  it  is  met  by  the  cardinal  objection 
that,  since  force  cannot  be  anniliilated,  the  o^iposite  current 
of  vapor,  which  simultaneously  transfers  an  equal  weight 
from  the  equator  to  the  pole  of  the  rotating  s^^here,  must, 
by  friction  or  contact  of  some  kind,  positively  return  the 
whole  of  the  mechanical  energy  expended  in  augmenting 
the  rotary  velocity  of  the  particles  of  water  moving  in  a 
contrary  direction.  This  n(>twithstanding,  we  must  accept 
the  fad  proved  by  the  dynamic  I'egister,  that  a  certain 
amount  of  mechanical  energy  disappears  when  the  rotating 
sphere  is  subjected  to  the  action  of  differential  temperatures. 
There  was  a  time  when  we  could  not  account  foi-  such  dis- 
appearance of  energy,  but — thanks  to  the  labors  of  Joule 
and  Mayer — the  mechanical  theoiy  of  heat  has  thrown  light 
on  the  subject.  The  theoreti^'al  deductions  of  Laplace  have 
lost  their  potency.  We  no  longer  confine  ourselves  to  the 
balance  anil  rule  in  measui'ing  the  result  of  exi^eiidcd  force. 
Joule    and    Mayer    have   taught   us   to   consult   also   the   titer- 


366  BADIANT  HEAT.  CHAP.  xxiT. 

mometer  during  our  iuvestigatious.  Bearing  in  mind,  then, 
■what  the  new  theoiy  of  heat  teaches,  the  disappearance  of 
mechanical  energy  during  the  experiments  with  the  dynamic 
register  ceases  to  l)e  a  puzzle.  Close  investigation  shows 
that  the  heat  resulting  from  the  arrested  motion  of  the  cir- 
culating vapor,  which,  on  leaving  the  aqueous  belt,  possesses 
a  rotary  velocity  equal  with  that  of  the  circumference  of 
the  sphere,  represents  A-ery  nearly  an  equivalent  of  the 
observed  loss  of  energy,  the  diiference  being  made  up  by 
heat  generated  by  the  particles  of  the  circulating  vajjor  as 
they  successively  impinge  against  the  minute  projections  of 
the  surface  of  the  convex  and  concave  spheres.  Obviously, 
the  heat  thus  generated  is  carried  off  l)y  the  cold  semi- 
spherical  casing  surrounding  the  sphere  of  the  dynamic 
register,  precisely  as  heat  produced  by  analogous  motions 
Avithiu  the  terrestrial  atmosphere  is  carried  off  by  radiation 
into  space.  In  either  case  the  heat  lost  is  an  equivalent  of 
the  mechanical  energy  abstracted  from  the  rotating  sphere. 

Illustrations  and  descriptions  have  been  prepared  explana- 
tory of  important  modifications  of  the  dynamic  register  deline- 
ated on  PI.  34,  adojited  in  order  to  control  the  irregular 
resistance  of  the  atmospheric  air  against  the  rotating  sphere, 
unavoidalde  in  employing  gas-flames  for  heating  the  equa- 
torial belt;  but  the  subject  having  already  occupied  too 
much  space,  I  now  propose  to  state  only  the  result  of  the 
experiments  which  have  been  made  with  the  modified  instru- 
ment, the  dimensions  of  which,  it  should  be  observed,  have 
been    considerably    increased,    the    motive    power,    however, 


CUAI".  xxii.  THE  EAlilWH  AXIAL  liOTATION.  367 

remaining  uucliangod.  It  is  iscarcely  necessary  to  remark 
that  a  complete  tlenumstratiou  and  record  of  an  investiga- 
tion of  this  complicated  nature  would  present  an  array  of 
figures  inadmissible  in  this  work.  The  diagram  on  PI.  oS 
has,  therefore,  been  devised  to  dispense  with  tigures ;  the 
relations  of  time,  velocity,  and  resistance  being  jjiesented  in 
sueli  a  manner  that,  among  other  facts,  the  aniduul  of  mechani- 
cal enei'gy  which  disappears  duiing  the  experiment  ma}'  be 
ascertained  by  mere  inspection.  For  the  [)urpose  of  saving 
space  and  facilitating  direct  comparison,  this  diagram  has, 
moreover,  been  so  arranged  that  the  iccord  of  the  experi- 
ments in  which  heat  and  refrigeration  have  been  employed 
is  placed  on  the  same  base-line  with  the  record  of  the 
experiments  in  which  difference  of  temperature  was  pre- 
sented. The  divisions  on  the  l)ase-liue  a  h  mark  the  time 
of  rotation,  the  large  spaces  indicating  minutes  and  the 
smaller  divisions  10  sec.  each.  The  length  of  the  ordinates 
of  the  curve  c  b  resting  on  the  base-line  represents  the 
number  of  turns  performed  in  a  given  time  when  the  rotat- 
ing sphere  is  not  subjected  to  the  action  of  heat  and 
refrigeration;  while  the  length  of  the  ordinates  of  the  curve 
d  e  represents  the  number  of  turns  when  heat  and  cold  are 
being  applied.  It  will  be  readily  perceived  that,  for 
instance,  the  ordinate  between  1  and  the  curve  c  b  repre- 
sents the  number  of  turns  per  minute  at  the  commencement 
of  the  second  minute,  while  the  ordinate  2  represents  the 
number  of  turns  per  minute  at  the  commencement  of  the 
third  minute,  and  so  on  for  all  the  other  ordinates. 


368  RABIAXT  HEAT.  chap.  xxil. 

The  'permanent  frictiou  of  the  instrument — i.e.,  the  friction 
of  tlie  pivot  on  -which  the  sphere  turns — being  practically 
inappreciable,  it  will  be  evident  that  the  resistance  ojjposing 
the  rotation  will  vary  in  the  ratio  of  the  square  of  the 
velocities.  Hence,  as  the  respective  ordiuates  between  the 
cui'ves  c  1)  and  d  e  and  the  base-line  represent  the  velocities, 
it  will  only  be  necessary  to  square  these  ordinates  in  order 
to  determine  the  exact  amount  of  resistance  to  the  periods 
indicated  bj^  the  divisions  on  the  base.  Accordingly,  the 
ordinates  mentioned  have  been  prolonged  in  the  ratio  of  their 
squares,  the  curves  /  Z>  and  g  e  being  the  result  of  this  pro- 
longation. Obviously,  the  lengths  of  the  ordinates  of  these 
curves  resting  on  the  line  a  h  represent  accurately  the  amount 
of  resistance  opposed  to  the  rotation  of  the  sphere  at  the 
times  indicated  by  their  intersection  with  that  line.  The 
rate  of  velocity — i.e.,  the  mimber  of  turns  per  minute  per- 
formed by  the  sphere  at  the  commencement  and  at  the 
termination  of  each  minute — will  be  found  by  referring 
to  the  figures  marked  on  the  vertical  lines  /  a  and  I  h. 
Thus,  for  instance,  the  rate  of  A^elocity  at  the  termination  of 
the  second  ininute  is  75.4  turns  Avhen  refrigeration  is  vot 
applied,  while  tlie  rate  is  68.0  when  the  cooling  medium  is 
applied  at  the  pole.  As  might  be  expected  from  the  irregu- 
lar nature  of  the  external  resistance  opposed  to  the  rotating 
mass,  the  curves  /  b  and  g  e  do  not  correspond  with  any  of 
the  conic  sections.  The  available  motive  power  of  2,540 
foot-grains  expended  during  the  experiment  is  represented  by 
the  supei-ficies  /  a  h,  the   energy  developed  being   represented 


CHAP.  XXII.  TBE  EAliTWS  AXIAL  ROTATION.  369 

by  the  superficies  g  a  e.  Assuuiing  the  former  to  be  1.000, 
tlie  latter,  as  shown  by  our  tliagraui,  will  be  0.763,  differ- 
ence =  0.237;  hence  the  amount  of  lost  energy  is  0.237  X 
2,540  =  601.98  foot-grains.  Now,  if  the  weight  of  ^\•ater 
which  is  condensed  at  the  pole  and  returned  to  the  equator, 
inulti])lied  by  the  height  necessaiy  to  generate  the  rotary 
velocity  acquired  during  the  transit,  should  amount  to  601.98 
foot-grains,  the  fact  will  be  established  that  the  current  of 
vapor  has  not,  during  its  passage  from  the  equator  to  the 
pole,  restored  any  of  the  energy  abstracted  from  the  sphere 
by  the  current  of  water  flowing  in  the  contraiy  direction. 
The  quantity  of  water  condensed  and  returned  to  the  equa- 
torial belt  being  readily  ascertained  by  observing  the  incre- 
ment of  temperature  of  the  contents  of  the  polar  cistern,  it 
is  easy  to  sho\v  that  the  energy  abstracted  from  the  rotating 
mass  by  the  water  thus  transferred  from  the  pole  to  the 
equator  corresponds  so  nearly  with  the  differential  mechanical 
energy  represented  by  the  superficies  f  g  e  b,  that  the  com- 
pensation resulting  from  the  tangential  force  exerted  by  the 
particles  of  the  currents  of  vapor  against  the  sui-face  of  the 
sphere  of  the  dynamic  register  is  inappreciable;  precisely  as 
we  find  that  the  compensating  tangential  force  of  the  cur- 
rents of  vapor  Avliich  sweep  over  the  basin  of  the  Mississippi 
from  west  to  east  (neuti-alized  by  the  currents  which  pass 
from  east  to  Avest)  is  an  inappreciable  fraction  of  the  retard- 
ing energy  of  19,836,000,000  foot-pounds  per  second,  exerted 
by  the  water  which  the  Mississippi  canies  in  the  direction 
of  the  equator. 


370  BABIANT  HEAT.  chap.  xxil. 

Having  thus  anal3^zed  the  opposing  energies  called  forth  by 
the  waters  flowing  toAvards  the  equator,  and  of  the  I'eturning 
vapors,  the  condensation  of  which  replenishes  the  river  basins, 
we  may  now  enter  on  a  computation  of  the  aggregate  amount 
of  the  retarding  energy,  and  the  consequent  diminution  of 
the  rotary  velocity,  of  the  earth,  caused  by  the  rivers  enume- 
rated in  the  preceding  table.  The  total  of  the  retarding  force 
entered  in  the  column  next  the  last,  it  will  be  found,  amounts 
to  53,857,788,300  foot-pounds  per  sec,  which  sum,  multiplied 
by  86,400  sec,  shows  that  the  earth  has  to  overcome  a 
resistance  of  4,653,313  X  10°  foot-pounds  during  each  revolu- 
tion. Multiplying  this  resistance  by  36,524  days,  we  ascertain 
that  the  retarding  energy  of  the  water  transferred  in  the 
direction  of  the  equator  by  the  entire  Southern  river  systems 
of  both  hemispheres  amounts  to  16,995,760,069  X  10"  foot- 
pounds in  a  century.  Now,  in  order  to  determine  the  dimi- 
nution of  rotary  velocity  consequent  on  this  counteracting 
energy,  it  will  be  indispensable  to  compute  the  earth's  rotary 
vis  viva.  The  elements  necessary  in  this  computation  are : 
volume,  time  of  revolution,  specific  gravity,  and  the  position 
of  the  centre  of  gyration  of  the  rotating  mass.  The  two 
first-named  elements  are  known  mth  desirable  accuracy ;  the 
third  element,  specific  gravity,  has  been  ascertained  Avith 
tolerable  accuracy;  but  the  position  of  the  centre  of  gyration, 
which  depends  on  the  internal  temperature  of  the  globe  and 
the  disposition  of  its  constituent  parts,  has  not  yet  been 
determined.  Physicists  assume  that  the  density  of  the  globe 
increases  towards  the  centre  in  arithmetical  progression ;  but 


CHAP.  XXII.  THE  EAirnra  aaial  uotation.  371 

this  assuraption  is  not  sustained  by  sound  reasoning.  Our 
space  not  admitting  of  discussing  this  complicated  question 
at  length,  let  us  merely  consider  the  leading  fact,  that,  at  a 
distance  of  only  -h  of  the  earth's  radius  =  1,0-14,400  ft.  from 
the  surface,  the  weight  of  a  superincumbent  mass  of  fused 
granite  will  exceed  900,000  lbs.  to  the  sq.  in.  =  60,000 
atmospheres.  Under  this  pressure  the  weight  of  air  will  be 
70  times  that  of  water,  and  3.5  times  that  of  the  heaviest 
metals.  Gold,  at  the  point  of  fusion,  is  7  times  heavier  than 
fused  granite,  while  neither  of  these  solids  loses  more  than 
Toir  of  specific  gravity  at  melting  heat — a  fact  which  proves 
conclusively  that  high  temperature  of  metals  and  minerals  is 
not  incompatible  with  great  density.  Hence  fused  granite, 
in  the  earth's  interior,  may  be  many  times  heavier  than  the 
cold  mineral  at  the  surface.  Unless,  therefore,  we  are  pre- 
pared to  dispute  the  assumption  that  fused  granite,  under  a 
pressure  of  900,000  lbs.  to  the  sq.  in.,  will  have  its  specific 
gravity  doubled — involving  a  density  less  than  one-third  of 
fused  gold  not  subjected  to  compression — we  must  admit 
that  the  specific  gravity  of  the  earth  at  the  depth  of  A  of 
the  radius  is  so  great  that,  if  the  density,  as  physicists  have 
assumed,  increases  in  arithmetical  progression  towards  the 
centre,  our  planet  Avould  be  many  times  heavier  than  it  is. 
We  are  compelled,  therefore,  to  reject  the  accepted  theory, 
more  especially  as  the  stated  enormous  pressure  consequent 
on  superincumbent  weight  takes  placer  at  only  ^  of  the 
earth's  radius  below  the  surface. 

In  accordance  with   the  foregoing   reasoning,  our    compu- 


373  RADIANT  HEAT.  chap.  xxii. 

tation  of  the  earth's  rotary  vis  viva  will  be  based  ou  the 
assumption  that  the  mass  is  homogeneous.  It  is  true  that 
the  specific  gravity  at  the  surface  is  somewhat  less  than 
one-half  that  of  the  entii'e  mass ;  but  we  have  sho^vn  that 
at  a  depth  of  iv  of  the  radius  from  the  surface  the  density 
is  so  great  that  if  it  continued  to  augment  in  arithmetical 
progression,  the  specific  gravity  of  the  globe  would  far  exceed 
that  which  has  been  determined  by  careful  investigation. 
Nor  should  we  lose  sight  of  the  important  fact  that  the 
temperature  corresponding  with  the  compression  produced 
by  the  superincumbent  weight  is  so  great  that  the  compo- 
nent parts  of  the  centi'al  mass  may  be  as  light  as  pumice, 
notwithstanding  the  enormous  external  pressure.  Conse- 
quently, it  may  be  satisfactorily  demonstrated  that  the 
earth's  circle  of  gyration  extends  considerably  beyond,  in 
place  of  being  within,  that  of  a  Jiomogeneous  sphere,  agree- 
ably to  the  accepted  theory  of  augmented  density  towards 
the  centre.  In  our  computations,  however,  we  will  assume 
that  the  circle  of  gyration  is  that  corresponding  -with  homo- 
geneity, which,  in  accordance  with  the  property  of  spheres, 
is  0.6325  of  the  great  circle.  Sir  John  Herschel's  determi- 
nation shows  that  the  mean  diameter  of  the  earth,  considered 
as  a  perfect  sphere,  is  7,912.41  statute  miles,  or  41,777,524  ft. ; 
hence,  if  we  assume  the  specific  gravity  to  be  5.5,  we  can 
readily  calculate  that  the  weight  is  1,308,608  X  10"  lbs. 
Multiplying  the  equatorial  velocity — 1,519.07  ft.  per  second 
— by  0.6325,  we  ascertain  that  the  mean  rotary  velocity  of 
the  entire  mass  of  the  earth  is  960.81  ft.  per  second — a  rate 


CHAP.  XXII.  TEE  EABTE'S  AXIAL  rxOTATION.  373 

acquired  by  a  fall  of  14,424  ft.  The  earth's  rotary  vis  viva 
will  accordingly  amount  to  14,424  X  1,308,008  X  10"  = 
18,875,361  X  10"  foot-pounds.  The  mind  being  utterly  in- 
capable of  conceiving  this  stupendous  energy  without  com- 
parison with  mechanical  energies  of  less  magnitude,  let  us 
ascertain  to  what  extent  it  will  be  diminished  by  the 
retardation  exhibited  in  the  tables  pre^^ously  presented — 
namely,  16,995,760,069  X  10'°  foot-pounds,  exerted  in  the 
course  of  a  century  by  the  southern  river  systems  of  both 
hemispheres.      Dividing  the  stated   retarding    energy  in  the 

, ,       .       .         ,  18,875,361  X  10"  ^    ,     , 

earths  v^s  viva,  thus:    i^.  995^760^069  X  lO"'    ''^  ^""'^   '^^"*' 

notwithstanding  the  enormous  amount  of  retardation  exerted 
in  a  centuiy,  only  1 1 1 0 e'u 0 00 0  of  the  rotary  energy  of  the 
earth  will  be  destroyed  in  that  time.  And  if  we  multiply 
the  fraction  thus  presented  by  10,000,  we  learn  that  at  the 
end  of  1,000,000  years  the  rotary  energy  of  the  earth  \\\[\ 
be  only  i\hiis  less  than  at  present !  By  no  other  compari- 
son, probably,  than  the  one  we  have  instituted  could  we 
clearly  comprehend  the  magnitude  of  18,875,361  X  10"  foot- 
pounds of  mechanical  energy. 

Let  us  now  calculate  the  effect  of  the  tabulated  resist- 
ance on  the  earth's  rotary  velocity  with  reference  to  time. 
The  retardation  observed  by  astronomers  being,  as  before 
stated,  about  12  sec.  in  a  century,  our  object  will  be  to 
ascertain  how  far  this  retardation  may  be  attributed  to  the 
counteracting  energy  under  consideration.  Multiplj'ing,  then, 
the  number   of   seconds  in  a  century,   3,155,673,600,  by   the 


374  EABIANT  KEAT.  CHAP.  xxii. 

retarding  energy  of  53,857,T80,300  foot-pounds  per  second, 
entered  in  the  table,  we  establish  the  fact  before  adverted 
to,  that  the  total  retardation  is  16,995,760,069  X  10'°  foot- 
ponnds  in  one  centniy.  Dividing  this  retardation  in  the  vis 
viva,  it  Avill  be  seen  that  the  earth  loses  mus^a^a^a  of  its 
rotary  energy  in  the  course  of  100  years ;  but  in  calculating 
the  time  corresponding  with  this  loss,  we  have  to  consider 
that  the  velocities  are  as  the  square  root  of  the  forces,  and 
that  consequently  the  rotary  velocity  will  not  be  reduced  as 
rapidly  as  the  rotary  energy.  Evidently,  if  the  diminution 
of  energy  and  velocity  corresponded  exactly,  the  retardation 
of   the  earth's  rotary  motion  during   one    century  would  be 

3,155,673,600        ^„,^  ,  -^  ^   .  ,  ui    ^i      i 

— =  2.8414  sec.     But,  m  accordance  with  the  laws 

1,110,592,343 

of  motion  referred  to,  the  diminution  of  velocity  during  the 
century  will  be  in  the  ratio  of  the  square  roots  of  the  earth's 
vis  viva  at  the  beginning  and  at  the  termination  of  that 
period.  Now,  this  ratio  being  readily  computed,  as  we  know 
the  amount  of  energy  lost  in  one  centuiy,  while  the  time  in 
seconds  is  also  known,  we  are  enabled  to  show,  by  an  easy 
calculation,  that  the  earth  suffers  a  retardation  of  1.42071 
sec.  Adding  the  retardation  occasioned  by  the  tabulated 
sedimentary  matter  =  0.00105  sec,  ascertained  in  the  manner 
explained,  the  total  retardation  of  the  earth's  rotary  velocity 
in  a  century,  at  the  presevt  epoch,  will  be  1.42176  sec.  The 
vastness  of  the  rotary  vis  viva  of  the  earth  having  already 
been  discussed,  it  will  not  be  necessary  to  offer  any  expla- 
nations   with   reference   to    the    insignificance   of   the    stated 


CUAP.  XXII.  THE  EARTWkS  AXIAL  liOTATION.  375 

retardation  in  comparison  witli  the  uiagnitutle  of  the  counter- 
acting energy  exerted  by  the  water  and  sediment  of  the  entire 
river  system  presented  in  our  tables. 

"We  have  now  to  consider  the  influence  on  the  eailh's 
rotary  energy  exercised  by  rivers,  the  course  of  which  is  in 
the  direction  of  the  poles.  Evidently  river  water  running 
from  the  equator  Avill  have  its  motion  round  the  axis  of 
rotation  continually  diminished  as  it  reaches  the  noi-thcrn 
parallels ;  hence  rotary  energy  will  be  imparted  to  the  earth 
by  all  rivers  flowing  towards  the  poles.  At  first  sight,  it 
will  be  imagined  that  the  energy  thus  imparted  will  neutra- 
lize the  retarding  force  exerted  by  the  waters  transferred 
towards  the  equator.  Certain  physical  causes,  however,  pie- 
vent  the  imparted  energy  from  restoring  any  of  the  earth's 
lost  vis  viva.  The  subject  will  be  most  readily  conq)rehend- 
ed  by  an  examination  of  the  nature  of  the  neutralizing  force 
exerted  by  the  following  great  rivers,  namely,  the  Lena, 
Yenesei,  Obi,  and  Mackenzie,  which  furnish  the  princij)al 
amount  of  water  discharged  into  the  Arctic  Ocean.  These 
rivers  drain  an  area  of  3,840,000  sq.  miles,  the  latitude  of 
the  centre  of  their  basins  and  their  outlets  being  very 
nearly  in  the  same  parallel.  The  mean  of  the  former  is  59 
deg.  30  min.,  that  of  the  latter  G9  deg.  56  min.  Accordingly, 
the  mean  circumferential  velocity  of  outlet  is  421.18  ft.  per 
second,  while  that  of  the  centre  of  basin  is  770.95  ft.  per 
second.  It  will  be  seen,  therefore,  that  a  diminution  of  rotary 
velocity  of  770.95  -  521.18  =  249.77,  say  250  ft.  per  second, 
takes  place  during  the  transfer  of  the  water  from  the  centre 


376  BADIANT  HEAT.  chap.  xxii. 

of  tlie  basins  of  these  rivei'S  to  tlieir  outlets.  Now,  a  velocity 
of  250  ft.  per  second  is  produced  by  a  fall  of  976.5  ft,  lience 
each  pound  of  M'ater  discharged  into  the  Arctic  Ocean  by 
the  before-named  rivers  •will  impaii;  a  mechanical  energy  of 
976.5  foot-pounds.  Apart  from  this  powerful  neutralizing 
force  of  a  given  weight,  the  quantity  of  water  ti-ansferred  is 
so  great,  owing  to  the  vast  extent  of  the  basins,  that,  uotAvith- 
standing  the  moderate  precipitation  in  high  latitudes,  the 
rotary  energy  imparted  to  the  earth  ^^•ill  balance  the  retarda- 
tion of  the  136  rivers  entered  in  our  tables.  It  scarcely 
requires  explanation  that  the  stated  enormous  force  exerted 
by  the  water  transferred  by  the  great  northern  rivers  is  owing 
to  the  rapid  diminution  of  rotary  velocity  in  approaching  the 
pole ;  a  single  degree  of  latitude  at  the  point  where,  for 
instance,  the  river  Lena  dischai'ges  into  the  Arctic  Sea  having 
a  greater  fall  than  te7i  degrees  have  within  the  tropics.  It 
would  be  waste  of  time,  however,  to  compute  the  exact 
amount  of  energy  imj)arted  to  the  earth  by  the  Arctic  livers, 
as  will  be  seen  by  the  following  examination  of  the  subject. 
Unquestionably,  if  the  supposed  pound  of  water,  on  entering 
the  Arctic  Ocean,  at  once  evaporates  and  ascends  into  the 
atmosphere,  we  must  admit  that  an  impulse  of  976.5  foot- 
pounds has  been  imparted  to  the  earth  by  its  transfer  from 
the  centre  of  the  river  basin;  but  if  it  should  be  found  that, 
in  place  of  evaporating  on  entering  the  cold  polar  sea,  the 
pound  of  water  commences  a  retrograde  motion  towards  the 
equator  through  Behring's  Straits  or  through  the  wide  channel 
bet\\'een  Norway  and  Greenland;  and  if  we  should  find,  also, 


CHAP.  XXII.  THE  EAllTWS  AXIAL  ROTATION.  377 

that  wLeu  it  crosses  the  59  deg.  30  rain,  parallel  (the  same 
as  that  of  the  centre  of  the  river  basin)  it  has  not  yet  been 
converted  into  vapor,  we  must  then  admit  that  the  whole 
of  the  energy  imparted  to  the  earth  by  the  ajyjyroacJi  towards 
the  axis  of  rotation,  during  the  original  transfer  to  the  polar 
sea,  has  been  completely  neutralized  by  the  retardation  con- 
sequent on  the  retreat  from  the  axis  of  rotation  during  the 
southerly  course  to  the  last-mentioned  latitude.  Following 
our  pound  of  water  during  the  continuation  of  the  motion 
towards  the  equator,  we  may  discover  that  it  has  not  changed 
its  form  into  vapor,  even  when  reaching  latitude  47  deg. 
45  min.,  at  which  point  the  circumferential  velocity  is  exactly 
250  ft.  per  second  greater  than  that  of  the  centre  of  the 
basin  from  whence  the  motion  proceeded.  In  that  case,  not 
only  has  the  imparted  energy  been  neutralized,  but  a  retarda- 
tion of  976.5  foot-pounds  has  been  called  forth  by  the  pound 
of  water,  the  course  of  which  may  possibly  continue  until 
it  mixes  wdth  the  warm  water  -within  the  tropics.  Let  us 
guard  against  confounding  the  movement  of  the  water  dis- 
charged into  the  Arctic  Sea  by  the  northern  rivei-s  with  the 
currents  produced  by  the  combined  influence  of  lunar  attrac- 
tion, wnds,  differential  oceanic  temperature,  and  solar  attrac- 
tion. It  has  long  been  recognized  that  the  water  poured 
into  the  Arctic  Sea  by  the  great  Asiatic  rivers  is  the  result 
of  condensation  of  vapors  raised  by  the  sun  within  or  near 
the  tropics.  A  corresponding  amount  of  water  must,  there- 
fore, be  returned  from  the  polar  sea,  or  its  surface  would  be 
elevated,  and  that  of  the  tropical  seas  suffer  a  proportionate 


378  BABIANT  HEAT.  chap.  xxii. 

depression.  The  reader  cannot  fail  to  perceive  the  important 
bearing  of  these  facts  on  the  question  of  retardation  of  the 
earth's  rotary  velocity. 

The  result  of  the  experiments  with  the  dynamic  register 
proves  that  the  rotary  motion  possessed  by  the  \'apors  on 
leaving  the  equatorial  seas  may  be  almost  entirely  destroyed 
by  being  converted  into  heat  during  their  course  towards  the 
basins  of  the  northern  rivers  ;  hence  imparting  no  perceptible 
tangential  force  to  the  earth.  Accordingly,  the  return  to  the 
tropical  seas  of  the  water  which  is  continually  being  dis- 
charged by  the  northern  rivers  into  the  polar  seas  will,  on 
account  of  the  increased  velocity  round  the  axis  of  rotation 
imparted  during  the  southern  course,  subject  the  earth  to  an 
amount  of  retardation  far  exceeding  that  produced  by  rivers 
flowing  towards  the  equator.  It  may  be  asked,  under  these 
circumstances,  why  the  latter  rivers  have  been  tabulated  and 
their  inferior  retarding  energy  calculated.  The  rivers  flow- 
ing in  the  direction  of  the  poles  have  been  examined,  tabu- 
lated, and  their  counteracting  energy  calculated ;  but  the 
question  of  attendant  retardation  of  rotary  velocity  cannot 
properly  be  entertained  until  certain  other  counteracting  in- 
fluences shall  have  been  examined.  The  publication  of  the 
table  containing  the  southern  rivers  has  been  deemed  neces- 
sary as  a  2Mini  (Vappui  facilitating  demonstrations  intended 
to  establish  the  fact  that,  independently  of  the  counteracting 
force  of  the  tidal  wave  (hitherto  greatly  overestimated),  the 
retarding  energy  called  forth  by  the  evaporation  within  the 
tropics,    and   the    consequent    condensation    and    precipitation 


CHAP.  XXII.  THE  EAUTira  AXIAL  ROTATION.  379 

in  the  temperate  zones,  fully  account  for  the  retardation  of 
the  earth's  rotary  velocity — 12  seconds  in  a  century — inferred 
fi'om  the  apparent  acceleration  of  the  moon's  mean  motion. 


The  fact  being  well  knoA\Ti,  through  European  and  Ame- 
rican publications,  that  the  results  attained  by  the  employ- 
ment of  the  instruments  described  in  the  foregoing  chapters 
rank  among  the  most  important  scientific  achievements  of 
the  latter  part  of  the  first  century  of  the  American  Republic, 
I  expected  that  the  Centennial  Commissioners  would  invite 
me  to  display  those  instruments  during  the  Exhibition,  and 
consequently  caused  tlie  same  to  be  repolished  and  arranged 
for  the  great  occasion.  It  is  proper  to  state  that,  although 
not  wanted  by  the  Commissioners,  the  time  spent  in  prepar- 
ing the  collection  lor  exliiljition  lias  not  been  wasted,  since 
it  is  my  intention  to  present  the  same  to  the  Smithsonian 
Institution,  after  the  completion  of  certain  investigations. 


CHAPTER   XXIII. 

DISTANCE  INSTRUMENT,* 

FOK    MEASURING    DISTANCES    AT   SEA.      (SEE   PLATE   36.) 


This  instrument  is  principally  intended  for  the  use  of  the 
naval  officer  iu  measuring  the  distance  of  an  enemy's  ship, 
to  enable  him  to  elevate  his  guns  with  precision.  Modern 
naval  tactics  being  principally  based  on  distant  firing,  an 
accurate  knowledge  of  the  object  to  be  aimed  at  becomes 
indis^jensable.  Any  device  for  obtaining  it  based  on  any 
process  of  calculation  is  evidently  out  of  the  question,  con- 
sidering that  a  single  minute  will  bring  two  approaching 
vessels,  moving  at  a  rate  of  ten  knots,  full  a  quarter  of  a 
mile  nearer  each  other.  In  firing  beyond  point-blank  range, 
therefore,  seconds  are  precious  in  determining  the  elevation 
of  the  guns.  Accordingly,  nothing  will  ausAver  short  of  an 
instrument  which,  by  a  single  observation  and  the  reading 
off  at  sight,  tells  the  distance.  The  instrument  under  con- 
sideration meets  these  somewhat  severe  conditions  perfectly, 

•  This  instniment  formed  part  of  the  original  equipment  of  the  steamship  Princeton. 


CHAP.  xxm. ' 


DISTANCE  INSTRUMENT.  381 


as  will  be  seen  by  tlic  following  explanation.     An  observer 
stationed  on  the  maintop  or  cross-tree  of  a  ^hip,  k)oking  at 
ji  vessel— say  a  mile  off— will  perceive  that  liis  line  of  vision, 
directed  to  the  horizon,  passes  over  the  point  marked  by  the 
water-line  of  the  hull,  and  he  will  also  perceive  that,  as  the 
vessel    approaches,    that    point    appears   to   sink    lower   and 
lower  below  the  line  directed  to  the  horizon;  in  other  words, 
the   angle  formed  by  that  line  and  the  line  directed  to  the 
water-line   of   the   approaching   vessel    continually    increases. 
On  the  other  hand,  if  the   vessel   recedes,  it   \\\\\   be   found 
gradually   to   diminish.      Now,    the    observer's   eye   (see   the 
plate   before   referred   to)  being  placed  at  a  definite  height 
above  the  level  of  the  sea,  and  his  line  of  vision  directed   to 
the  horizon  being  the  tangent  of  the  earth's  curvature  pass- 
ing through  the  definite  point  a,  it  follows  that  the  angles 
h  a  c  and  (/  a  c,  respectively,  will  determine  the  distance  of 
h  and  g  from  h,  when  vertical  to  a.     Now,  the  earth's  cui-va- 
ture  is  constant,  the  height  of  a  above  the  level  of  the  sea 
is  knoAvn,   and  the  angles  h   a  c,  etc.,  may  be  readily  mea- 
sured b}-  reflectors  and  the  graduated  arc.     But  there  is  no 
time  for  mathematical  computation. 

The  Distance  Instrument,  it  will  be  seen  by  the  following 
description,  performs  the  required  computation  with  unemng 
certainty  whilst  the  observer  measures  the  angle,  and  it 
exhibits  the  result  the  instant  he  has  pei-formed  his  part. 
Every  one  familiar  with  nautical  instniments  will,  by  an 
attentive  inspection  of  the  drawing,  readily  understand  its 
principle  and  operation;  a  very  brief  description  will  there- 


382  DISTANCE  INSTRUMENT.  chap,  xxiii. 

fore  suffice.  A  is  an  ordinary  reiiector,  as  used  in  quadrants ; 
B,  the  object-glass,  and  C,  tlie  sight  by  which  the  angles  //  a  e, 
etc.,  are  measured ;  D,  a  spindle,  to  the  end  of  which  the 
reflector  is  firmly  attached  ;  E,  lever  for  turning  said  spindle ; 
F,  sliding-nut  made  to  move  freely  up  and  down  in  a  slot 
at  the  lower  end  of  lever  E ;  G,  thumbscrew  worldng  in  the 
sliding-nut ;  H,  pinion  on  said  screw,  working  into  cogs  cut 
in  the  circumference  of  a  graduated  index-plate  J ;  K,  socket 
sliding  on  the  main  stem  of  the  instrument  and  supporting 
the  frame  and  centre  of  the  revolving  index-plate.  Before 
noticing  the  operation  of  the  instniment,  it  will  be  necessary 
to  point  oxit  the  manner  of  graduating  the  index-plate. 
Considering  the  extent  of  the  point-blank  range  of  naval 
ordnance,  it  is  evident  that  no  distance  under  400  yards  need 
be  measured :  supposing,  therefore,  that  Ti  is  400  yards  dis- 
tant fi'om  h,  it  will  be  seen  that  the  operation  or  I'ange  of 
the  instrument  will  be  limited  to  the  angle  A  a  c,  which  thus 
determines  the  extent  of  movement  or  vibration  of  the  lever 
E.  This  movement  again  determines  the  pitch  of  the  thumb- 
screw and  the  relative  diameter  of  the  pinion,  it  being  evident 
that  the  extreme  vibration  of  lever  E  should  not  produce 
more  than  one  revolution  of  the  index-j)late.  Any  con- 
venient-sized index-plate  being  selected,  a  scale  graduated 
into  feet  or  yards  is  then  constructed,  corresponding  to  the 
circumference  of  the  plate ;  the  mode  of  dividing  the  scale 
being  as  follows:  In  the  first  place,  a  base-line  of  100  feet 
(represented  hj  a  b  in  the  diagram)  is  supposed,  and  the 
tangent  a  c  determined  accordingly.     The  known  curve  b  d  c 


CHAP.  XXIII.  DISTANCE  IXSTFUilENT.  383 

is  tlieu  divided  into  spaces  h  (/,  </f,fe,  etc.,  of  10  yards  eacli, 
comraenciug  at  a  point,  I>,  400  yards  from  b.  The  sines  of 
the  angles  7i  a  c,  g  a  c,  etc.,  are  next  calculated  and  marked 
on  the  before-mentioned  scale,  and  from  thence  ultimately 
transferred  to  the  curved  scale  on  the  index-plate.  The  fol- 
lowing directions  for  using  the  instrument  are  deemed  sufK- 
cient :  Turn  the  thumbscrew  until  the  line  maiked  ''  horizon  " 
is  placed  directly  under  the  fixed  index.  Then  adjust  the 
oljject-glass  by  means  of  the  set  screw  M,  so  that  the  real 
and  reflected  horizons  come  in  a  line.  This  adjustment  being 
made,  the  instrument  is  ready  for  use,  and  need  not  be 
readjusted  unless  disturbed.  The  process  of  measuring  the 
distance  consists  simply  in  turning  the  thumbscrew  G  until 
the  reflected  water-line  of  the  object  observed  is  brought  in 
a  line  watli  the  real  horizon  seen  through  the  object-glass. 
The  point  on  the  scale  of  the  index-plate  placed  directly 
under  the  fixed  index  shows  the  distance  desired.  It  must 
be  conceded,  on  theoretical  considerations,  that  if  the  base- 
line be  previously  known  and  the  instniment  made  to  cor- 
respond thereto,  the  measurement  cannot  fail  to  be  accurate ; 
but  such  is  the  nature  of  this  base-line  that  it  cannot  be 
previously  known ;  accordingly,  the  base-scale  L  has  been 
introduced,  by  which  the  instrument  may  at  all  times  be 
made  to  conform  to  the  variable  height  of  the  base.  It 
is  evident  that  an  increase  of  altitude  would  render  the 
scale  of  the  index-plate  too  short,  and,  on  the  other  hand, 
too  long  if  the  altitude  be  diminished.  It  is  also  evident 
that    by    sliding    the    index-plate    up,    the    effect    of    which 


384  DISTANCE  TNSTBUMENT.  chap,  xxiii. 

will  be  to  shorten  the  lever  E,  any  diminution  of  the 
base  may  be  compensated  for,  and  the  index-plate  remain 
very  nearly  correct.  The  sliding  the  index  down  would  in 
like  manner  compensate  for  any  increase  of  the  base.  On 
mathematical  considerations,  it  is  obvious,  however,  that  this 
mode  of  compensating  for  variations  of  the  base  cannot  be 
carried  very  far.  Index-plates  of  different  graduations  will, 
therefore,  be  employed  to  suit  the  height  of  the  masts  of 
different  classes  of  vessels,  and  the  base-scale  only  resorted 
to  for  compensation  to  meet  irregularities  occasioned  by 
altered  draught  of  water,  consequent  on  diminution  of  ammu- 
nition, stores,  etc.  At  first  sight,  it  would  appear  that  the 
base  employed  in  this  instrument  is  not  sufficiently  definite 
or  accurate ;  on  due  consideration,  however,  it  will  be  found 
to  be  fully  as  definite  as  required. 

In  the  first  place,  the  height  of  the  maintop,  cross-tree,  or 
other  point  of  a  shiji  above  the  bottom  of  the  keel  may  be 
ascertained  to  an  inch,  and,  when  once  known,  may  be  re- 
corded, as  well  as  tonnage,  length,  beam,  etc.  Secondly,  the 
draught  of  water  amidships  is  ahvays  known  to  a  careful 
commander,  within  two  inches  or  less.  Tlie  draught  of  water, 
being  deducted  from  the  height  above  the  keel,  establishes 
the  altitude  above  the  water-line.  The  height  of  the  obser- 
ver's eye — ordinarily  five  feet  six  inches — being  next  added, 
determines  the  base  Avithin  an  inch  or  two.  So  far,  then, 
the  accuracy  is  all  that  can  be  desired  for  practical  pur- 
poses. The  effect  of  the  rolling  of  the  ship,  Avhich  at  sea 
always  takes  place  to  some  extent,  next  demands   attention. 


cuAi'.  xxiii.  uiiiTAMi:  lysxnuMEyr.  385 

It  would  be  au  extreme  ciise  to  suppose  the  observer  tossed 
through  uu  arc  of  20  feet  whikt  taking  au  observation — viz., 
10  feet  on  each  side  of  the  vertical  line.  On  cakuhition,  it 
will  be  found  that  sucdi  oscillati(tu  would  t>nly  produce  a 
depression  of  six  inches  at  the  loiccd  point.  Finally,  the 
rising  and  falling  of  the  sliip  deserves  to  be  noticed.  The 
vertical  movement  of  the  inidaliip  hoilij,  being  at  all  times 
surprisingly  small,  \vill  be  found  quite  unimportant  at  times 
when  the  Distance  Instrument  is  likely  to  be  wanted.  Again, 
as  each  observation  only  i-equires  a  feAV  sect)nds,  it  may  be 
frc(piently  repeated.  It  is  proper  to  add  that  an  error  <»f 
6  inches  in  a  base  of  100  feet,  and  which  will  not  ordi- 
narily occur,  only  causes  an  error  of  distance  of  nine  yards 
in  a  mile. 


CHAPTER  XXIY. 

THE  STEAM  FIEE-ENGINE. 
(SEE   PLATE   37.) 


The  Mechanics'  Institute  of  New  York  offered  its  great 
gold  medal,  in  January,  1840,  as  a  prize  for  the  best  plan 
of  a  steam  fire-engine.  Having  several  years  previously  de- 
signed such  machines  in  England,  among  which  may  be 
mentioned  the  steam  fire-engine  employed  during  the  mem- 
orable fire  at  the  Argyle  Rooms  in  London,  in  1830  (the 
first  time  fii-e  had  ever  been  extinguished  by  the  mechanical 
power  called  forth  by  fire),  I  had  no  difficulty  in  producing 
plans  complying  with  the  conditions  of  the  Mechanics'  In- 
stitute in  a  manner  warranting  the  award  of  the  prize 
offered. 

The  following  description — reference  being  had  to  the 
illustration  on  PI.  37 — shows  the  detail  of  the  steam  fire- 
engine  thus  accepted  by  the  Mechanics'  Institute  of  New 
York.     A,  double-acting  force-pump,  composed  of  gun-metal, 


CHAP.  XXIV.  THE  STEAM  FIHE-EXGINE.  387 

firmly  secured  to  the  carriage-frame  by  four  strong  brackets 
cast  on  its  sides ;  a  a,  suction-valves ;  a'  a',  suction-passages 
leading  to  tlie  cylinder;  a",  clianibur  containing  the  suction- 
valves,  to  which  chamber  are  connected  suction-pipes  a'"  a'", 
the  hose  being  attached  to  the  latter  by  screw-couplings  in 
the  usual  manner,  and  closed  by  the  ordinary  screw-cap. 
Tlie  delivery-valves  and  passages  at  the  top  of  the  force- 
pump  are  similar  to  the  suction-valves  and  passages  men- 
tioned. B,  the  air-vessel,  composed  of  copper,  its  form  being 
spherical ;  l>  h,  delivery-pipes,  to  which  the  hose  is  attached. 
"Wlu'u  only  one  jet  is  required,  the  opposite  pipe  may  be 
closed  by  a  screw-cap,  as  usual.  The  piston  of  the  force- 
pump  is  provided  with  double  leather  packing,  the  piston- 
rod  being  nuide  of  copper.  C,  boiler,  constructed  on  the 
liiineiple  of  the  oi'dinary  locomotive  boiler,  containing  an 
adequate  number  of  tubes  of  suitable  diameter.  The  top  of 
the  steam-chamber  and  the  horizontal  part  of  the  boiler  is 
covered  w'ith  wood  as  usual,  in  order  to  prevent  loss  of  heat 
by  radiation,  c,  fire-door ;  c',  ash-pan ;  c",  box  attached  to 
end  of  boiler,  enclosing  the  exit  of  the  tubes.  The  hot  air 
from  the  tubes  entering  this  box  is  passed  off  through  a 
smoke-pipe  c'",  the  exit  of  which  makes  a  half-spiral  turn 
round  the  air-vessel,  as  shown  in  the  illustration,  e"",  iron 
brackets,  riveted  to  the  boiler  and  supported  by  the  carriage- 
frame.  C'*,  a  wrought-iron  brace,  bolted  to  the  carriage-frame, 
for  supporting  the  horizontal  part  of  the  boiler.  E,  vertical 
])ipe  attached  to  the  top  of  the  steam-chamber,  containing 
a   conical    steam-valve   e,   and    also   the    safety-valve   e'  /    e", 


388  THE  STEAM  FIBE-ENGINE.  chap.  xxiv. 

regulating  screw  and  handle,  connected  to  the  steam-valve, 
for  admitting  or  shutting  off  the  steam  ;  <?'",  induction-pipe 
for  conveying  the  steam  from  the  boiler.  F,  doul)le-actin_f 
working  cylinder,  provided  -with  steam-passages  and  slide- 
valve  of  the  usual  construction  ;  it  is  firmly  secured  to  the 
carriage-frame  by  means  of  brackets,  in  the  same  manner  as 
the  force-pump.  /,  eduction-pipe,  for  cariying  oft"  the  steam 
to  the  atmosphere  ;  /',  piston,  provided  -with  metallic  pack- 
ing on  Barton's  plan ;  /",  piston-rod  of  steel,  attached  to 
the  piston-rod  of  the  force-j)ump)  by  means  of  the  cross-head 
G,  composed  of  Avrought  iron ;  both  piston-rods  being  in- 
serted into  the  said  cross-head  and  secured  by  keys,  g, 
tappet-rod,  attached  to  the  cross-head,  for  moving  the  slide- 
valve  of  the  steam-cylinder  by  means  of  the  nuts  g'  </'.  The 
latter  may  be  placed  at  any  desirable  position  on  the  tajipet- 
rod,  to  ensure  a  regular  action  of  the  valve.  A  short  axle 
of  wrought  iron,  turning  in  bearings  attached  to  the  cover 
of  the  steam-cylinder,  operates  the  steam-valve  by  appro- 
priate levers  acted  ujion  alternately  by  the  nuts  g'  g'.  I, 
feed-pumjj  for  supplying  the  boiler,  provided  with  spindle- 
valves  on  the  ordinary  plan,  its  suctiou-pijie  communicating 
with  the  valve-chamber  of  the  force-pump,  the  feed-^witer 
being  carried  into  the  horizontal  part  of  the  Ijoiler.  /, 
plunger  of  the  force-pump,  composed  of  gun-metal  or  copper, 
attached  to  the  cross-head  G. 

Before  proceeding  with  the  description,  it  will  be  neces- 
sary to  state  that,  although  the  efficiency  of  the  "  steam-blast " 
was  well  ascertained  at  the  time,  the  prevailing  opinion  that, 


CHAP.  XXIV.  77//:   STEAM   I'lHE-EXdlXE.  389 

in  (••niiiiKHi  witli  the  Int-oiuotive  engine,  red-hot  sparks  would 
eiiiauatc  fr<iiii  a  steam  tire-engine,  and  prove  dangerous  among 
houses  in  a  elose-lmilt  eity,  I  was  compelled  to  resort  to 
the  employment  of  a  blowing  apparatus  for  generating  the 
neeessarily  large  (piantity  of  steam  indispensable  to  render 
the  machine  efficient. 

J,  blowing  ap[iaratus,  consisting  of  a  square  wooden 
bo.\,  with  panelled  si<les,  in  which  a  thin  s(piare  piston  _/'  is 
applied,  leather  packing  being  employed  to  make  air-tight 
joints.  J,  circular  holes  through  the  sides  for  admitting 
atmospheric  air  into  the  box,  these  holes  being  covered  on 
the  inside  by  pieces  of  leather  or  India-rubber  cloth  acting 
as  valves,  j",  similar  holes  through  the  top  of  the  box  for 
passing  off  the  air,  at  each  stioke  of  the  i)iston,  into  the 
receiver  or  regulator  K,  which  is  provided  with  a  movable 
top  I:  The  latter  is  com])osed  of  wood,  joined  by  leather 
to  the  upper  part  of  the  box,  a  thin  sheet  of  lead  being 
attached  thereto,  in  order  to  keep  up  a  certain  pressure  of 
air  in  the  regulator.  k\  channel  made  of  sheet-iron,  attached 
to  the  lilowing  apparatus,  communicating  freely  with  the 
regulator  K.  To  the  said  channel  is  connected  a  conducting- 
pipe,  marke<l  by  dotted  lines  in  the  longitudinal  section  of 
the  engine,  for  conveying  the  air  from  the  receiver  into  the 
a-sh-pan  under  the  furnace  of  the  boiler  at  l-'.  The  con- 
ducting-pipe,  it  should  be  ol)served,  passes  along  the  inside 
()f  the  carriage-frame  on  either  side. 

L  L,  parallel  iron  rods,  to  which  the  piston  of  the  blow- 
ing apparatus  is  attached.     These  rods  work  thiough  guide- 


390  THE  STEAM  FIBE-EKGINE.  chap.  xxiv. 

brasses  /  I,  and  may  be  attached  to  the  cross-bead  G  l)y  keys 
at  I'  v.  The  holes  at  the  end  of  the  said  cross-head  admitting 
these  rods  are  sufficiently  large  to  allow  a  free  movement 
"whenever  it  is  desirable  to  woi'k  the  blowing  apparatus  inde- 
pendently of  the  engine.  M,  spindle  of  wrought  iron,  placed 
transversely,  turning  in  bearings  fixed  under  the  carriage- 
frame.  To  this  spindle  are  fixed  two  crank-levers  m  m, 
which,  by  means  of  two  connecting-rods  m'  m',  give  motion 
to  the  rods  L  L  attached  to  the  piston  of  the  blowing  appa- 
ratus. 

N,  crank-lever  secured  to  the  end  of  spindle  M,  which, 
by  ineans  of  a  connecting-rod  applied  to  a  crank-pin,  fixed 
in  the  hub  of  the  carriage-wheel,  on  the  outside,  will  com- 
municate motion  to  the  blowing  apparatus  whenever  the 
carriage  is  in  motion.  By  this  simple  expedient  a  powerful 
combustion  will  be  kept  up  in  the  boiler  furnace  while  the 
engine  is  on  its  way  to  the  place  of  conflagration.  By  de- 
taching the  connecting-rod  referred  to,  and  applying  a  hand- 
lever  to  N,  the  blowing  apparatus  may  be  operated  by 
manual  labor.  The  carriage-frame  should  be  made  of  oak, 
plated  with  iron  all  over  the  outside  ;  the  top  plate  to  have 
small  recesses,  as  shown  in  the  drawing.  The  lock  of  the 
carriage,  axles,  and  springs  to  be  made  as  usual,  only  differ- 
ing by  having  the  large  springs  suspended  below  the  axle. 
The  carriage-wheels  to  be  constructed  on  the  suspension  prin- 
ciple ;  spokes  and  outside  of  rim  to  be  made  of  wrought 
iron,  very  light. 


CHAPTER    XXY. 

THE   STEAM-SHIP   PRINCETON. 
(SEE   PLATES   38,    39,    AND    40.) 


In  the  sixty-sixth  year  of  the  American  Rejiublic — 1842 
— the  first  steam  ship-of-wai-  provided  -witli  a  submerged  j^ro- 
peller  and  steam  machinery  located  below  water-line  was 
built  at  Philadelphia.  Complete  success  attended  this  under- 
taking, as  will  be  seen  from  the  following  extract  from  a 
speech  delivered  in  the  Senate  of  the  United  States  by  Sena- 
tor Mallory,  of  Florida,  May  14,  1858  : 

"In  1839  Congress  authorized  the  construction  of  three 
war-ships.  In  1840  the  Secretaiy  of  the  Kavy,  in  obedience 
to  that  law,  ordered  two  to  be  constructed.  There  were  two 
plans  at  that  time.  The  question  of  whether  steam  could  or 
could  not  be  successfully  applied  to  war-vessels  had  not  then 
been  solved  ;  the  fear  of  danger  from  ignition  by  fire  pi-e- 
vailed  in  the  minds  of  all  naval  men,  and  the  problem  Avas 
to  be  solved.      Its   solution   was   demanded   by   every  naval 


392  THE  STEAM-SUir  FUmCEIOX.  chap.  xxv. 

power  on  earth.  One  of  the  officers  of  our  navy,  Captain 
William  Plimter,  submitted  a  plan  by  which  wheels  were  to 
be  inserted  in  the  bilge  of  the  vessel  on  each  side— s\ib- 
merged  wheels.  Ericsson  had  demonstrated  his  plan  to  be 
feasible,  practicable,  and  just,  already.  This  "was  no  experi- 
ment in  the  Princeton.  The  experiment  had  been  made  at 
great  cost  by  Captain  Ericsson.  .  .  .  The  Secretary  of 
the  Navy,  in  authorizing  the  construction  of  these  two  ves- 
sels, directed  one  to  be  constructed  on  Hunter's  plan — not 
model,  as  the  Senator  from  Michigan  says  ;  the  model  -was 
not  in  cpxestion  at  all ;  our  models  were  as  good  then  as 
they  are  now ;  but  the  point  Avas  the  application  of  steam 
to  naval  purposes.  One  was  to  be  built  on  Eilcsson's  plan, 
and  one  on  Hunter's  plan.  Hunter's  plan  proved  a  total 
failure ;  Ericsson's  plan  laid  the  foundation  of  the  present 
steam  marine.  She  was  the  first  war  propeller  ever  built  on 
the  face  of  the  earth.  In  the  Princtton  he  brought  for\\  ard 
not  only  his  propeller  invented  by  himself,  but  a  great 
many  appliances  appurtenant  to  steam  navigation  which 
have  since  been  used  in  our  service. 

"Now,  to  show  the  estimate  in  which  this  shiji  was  held, 
I  will  mention  that  the  American  Institute,  hearing  of  it, 
sent  a  committee  to  investigate  the  condition  and  success  of 
what  they  deemed  an  experiment.  I  will  not  read  the  whole 
irport  I  if  the  committee  of  the  American  Institute.  My  j^ur- 
pose  here  is  to  shoAV  the  value  of  Captain  Ericsson's  services 
to  our  country.  The  committee  conclude  by  saying,  after 
summing  up  the  speed  of  thirteen  knots: 


CHAP.  XXV.  TE£  STEAM- SUIl'  PRINCETON.  393 

"'In  coucliisiou,  your  committee  beg  leave  to  present  the 
Princeton  as  every  way  worthy  of  tlie  highest  honors  of  this 
Institute.  She  is  a  sublime  conception,  most  successfully 
realized,  an  effort  of  genius  skilfully  executed,  a  grand, 
unique  combination,  honorable  to  the  country  as  creditable 
to  all  engaged  upon  her.' 

"This  is  signed  by  ten  members  of  the  Institute.  Fur- 
ther to  illustrate :  Cai^tain  Stockton,  in  1844,  after  describing 
the  ship,  her  guns  and  her  arniameut,  says  everything  human 
language  can  to  extol  her  in  the  eyes  of  the  American 
people.  As  I  said,  the  Princeton  is  the  foundation  of  om* 
present  steam  marine.  It  is  the  foimdation  of  the  steam 
marine  of  the  whole  world.  She  created  universal  surprise 
w^herever  she  was  seen.  She  revolutionized  naval  vessels ; 
and  hereafter,  in  maritime  war,  those  who  send  sailing  vessels 
to  sea  send  them  but  to  be  captui-ed." 

The  following  extract  from  the  work  on  "  Naval  and  Mail 
Steamers,"  published  1853  by  Charles  B.  Stuart,  Engineer- 
in-Chief  of  the  United  States  Navy,  furnishes  some  imijortaut 
particulars  relating  to  the  Princeton : 

"This  vessel  was  designed  by,  and  constructed  under  the 
superintendence  of.  Captain  John  Ericsson,  of  New  York. 


Length  on  deck,    .... 
Length  between  perpendiculars,    . 
Extreme  beam  on  deck. 
Depth  of  lower  hold  to  berth-deck. 
Depth  from  berth  to  spar-deck,    . 


164  feet 

150 

(f 

30 

(1 

G  inches 

14 

(1 

7 

u 

6       " 

TON. 

CHAr.   XXV. 

21 

feet  6  inches. 

GTo 

tons. 

418 

a 

954 

ii 

1,04G 

11 

gl^t, 

346  square  ft. 

390 

394  THE  aiEAM-SUIF  FmyCHTON. 

Total  deptli  of  vessel,  . 

Measurement  burthen,  . 

Launching  ■weight  of  hull,    . 

Displacement  at  IG^  feet  draught, 

Displacement  at  IS  feet  draught, 

Immersed  midship  section  at  IG^  feet  draught, 

a  a  a  jg 

Draught  of  water  at  deepest  load,  with  200 

tons  of  coal  on  board,  .         .         .         .19  feet  4  inches. 

Draught  of  water  with  100  tons  of  coal  ^     ,.  ,,.„,., 

^  .  .  forward,  14f  feet, 

in,  after-bunkers  and  provisions,  and   ,- 

aft,  18i     " 

water  for  the  crew,  half  out,  J 

Mean  draught  of  water  with  half  coal  out, 

and  all  other  weights  full,  .  .  .  17  feet. 
"The  peculiarity  of  model  consisted  in  a  ver^^  flat  floor 
amidships,  with  great  sharpness  forward  and  excessive  lean- 
ness aft,  the  I'un  being  remarkably  fine,  Avith  a  great  extent 
of  dead-wood  terminating  in  a  stern-post  of  the  unusual 
thickness  of  twenty-six  inches  at  the  centre  of  the  propeller- 
shaft,  but  tapering  above  and  below.  This  dead-\vood  and 
stern-post  was  pierced  by  a  hole  thirteen  inches  diameter  for 
the  passage  of  the  propeller-shaft.  The  stern,  measuring  from 
a  perpendicular  from  the  aft  end  of  the  spar-deck,  overhung 
the  stern-post  fifteen  and  one-half  feet,  and  depending  from 
it  was  a  false  stern-post,  leaving  a  space  of  six  feet,  fore  and 
aft,  between  it  and  the  true  stern-post.  The  pi'opeller  (four- 
teen feet  in  diameter,  composed  of  bronze,  with  six  propeller- 
blades,  pitch  thirty-five  feet)   was  placed  within  this  space. 


CUAP.  XXV.  THE  STEAMSHIP  PRIXGETO^i.  395 

The  false  stern-post,  or  rudder-post,  was  composed  of  a 
wrougbt-irou  bar,  covered  witli  half-inch-tluck  copper  plate  ; 
it  was  attached  at  top  by  brass  flanges  to  a  strong  oak  knee, 
securely  bolted  tct  the  counter  of  the  vessel ;  the  lower  part 
of  it  was  attached  by  similar  flanges  to  a  solid  oak  timber 
placed  as  a  continuation  of  the  keel  beyond  the  true  stern- 
post  ;  this  timber  was  fourteen  inches  deep,  and  securely 
boltt'tl  to  the  keel  and  dead-wood.  The  metallic  false  stern- 
post  was  five  and  three-eighths  inches  broad  athwart  ship, 
and  t\vo  feet  long  fore  and  aft;  the  forward  part  was  brought 
to  an  acute  angle  to  diminish  its  resistance  to  the  water, 
wliilf  its  after-part  was  square  to  receive  the  attachment  of 
the  rudder.  The  rudder  was  also  composite  in  its  construc- 
tion, being  formed  of  a  wrought-iron  frame,  the  interstices  of 
which  were  filled  in  with  pieces  of  five-inch-thick  pine  plank, 
the  Avhole  cased  over  with  a  copper  plate  three-sixteenths  of 
an  inch  thick.  The  thickness  of  the  rudder  athwart  ship  was 
the  same  as  that  of  the  false  stern-post,  viz.,  five  and  three- 
eighths  inches. 

ENGHiTES. 

"The  semi-cylinder  engine  of  the  Princeton  is  unquestion- 
ably the  most  remaikable  modification  of  the  steam-engine 
that  has  ever  been  carrii'd  into  successful  practice.  A  vibrat- 
ing piston  of  a  rectangular  form  moving  in  a  semi-cylinder 
is  an  old  mechanical  device.  Mr.  Watt,  in  his  celebi-ated 
patent,  embraced  this  plan  for  transmitting  the  motive  force 
of  steam  to  maohineiy.  Siuce  liis  time  several  engineers  liave 
attempted  to  buihl  engines  on  this  plan,  but  without  succes.s. 


396  THE  STEAMSHIP  PBINCETOW.  chap.  xxv. 

In  common  witli  Mr.  Watt,  they  have  adopted  the  single 
semi-cylinder  with  packing  against  the  piston-shaft.  Erics- 
son's plan  differs  materially  from  these  various  attempts,  he 
having  introduced  double  or  compound  semi-cylinders  of  dif- 
ferent diameters,  with  double  pistons  placed  in  opposite  direc- 
tions on  the  piston-shaft,  both  being  acted  upon  by  the  steam 
at  the  same  time,  their  differential  force  being  the  effective 
motive  power  of  the  engine.  The  combination  of  two  such 
double  semi-cylinders,  arranged  so  as  to  transmit  their  power 
in  directions  nearly  rectangular  to  a  crank-pin  common  to 
both,  also  contributes  to  the  complete  success  of  this  singular 
engine. 

"By  reference  to  the  plate,  it  will  be  seen  that  the  upper 
semi-cylinder,  which  contains  the  reacting  piston,  is  twenty 
inches  in  diameter,  the  lower  or  working  semi-cylinder  being 
seventy-two  inches  diameter,  both  ninetj^-six  inches  long  in 
the  clear.  The  radius  of  the  reacting  piston,  being  deducted 
from  that  of  the  working  piston,  leaving  twenty-six  inches 
effective  Avidth  of  piston,  with  its  centre  of  pressure  placed 
10  +  13  =  23  inches  from  the  centre  of  the  piston  shaft. 
The  active  piston  area  will  thus  be  26  X  96  =  2,516  super- 
ficial inches,  moving  at  a  mean  distance  of  twenty-three  inches 
from  the  centre  through  an  arc  of  ninety  degrees. 

"  On  close  examination  this  engine  will  be  found  to  pos- 
sess many  peculiar  properties,  some  of  which  merit  particular 
notice.  The  vibration  of  the  working  piston  will  be  found 
to  correspond  nearly  to  the  beat  of  the  pendulum,  and  thus, 
unlike  the  ordinaiy  engine,  the  return  movement  of  the  piston 


CHAP.  XXV.  THE  STEAM-Snir  PRINCETON.  397 

at  each  termiiiatiou  of  the  stroke  is  materially  assisted  by 
the  force  of  gravity.  An  undue  accumulation  of  condensed 
water  on  the  piston,  so  difficult  to  carry  off  in  the  ordinary 
engine,  presents  no  inconvenience  here,  as  the  inclined  posi- 
tion of  the  piston  allows  the  condensed  water  to  flow  gradu- 
ally down  into  the  steam-passages  before  the  piston  reaches 
the  termination  of  the  stroke.  The  outward  tendency  of  the 
packings,  induced  by  centrifugal  force,  assists  materially  in 
forming  tight  joints,  the  main  packing  being  held  out  by  the 
force  of  gravity.  The  lateral  yielding  of  the  piston-shaft, 
caused  by  the  pressure  of  the  steam  on  opening  the  inlet- 
valve,  tends  to  give  additional  tightness  to  the  packings,  the 
pistons  being  forced  into  reduced  radial  limits  by  the  yielding 
alluded  to.  The  crank-levers  attached  to  the  piston-shafts 
being  placed  nearly  in  the  same  position  with  the  main 
pistons,  it  will  be  found  that  the  crank-journals  of  those 
shafts  are  relieved  from  j^ressurc,  on  principles  analogous 
to  the  i-elieving  of  water-wheel  journals,  by  transmitting  tlie 
power  at  some  point  near  the  centre  of  pressure.  The  increase 
of  force  imparted  to  the  crank-pin  at  each  half-turn  of  the 
main  crank,  owing  to  the  angular  position  of  the  piston-rod 
ci-anks,  and  happening,  as  it  does,  when  the  former  presents 
short  leverage,  is  a  marked  feature  of  this  engine. 

"The  small  angular  movement  (ninety  degrees)  of  the 
main  piston  .also  deserves  attention.  A  greater  motion,  while 
it  would  augment  the  power  of  any  given-sized  cylinder, 
would  cause  undue  strain  on  all  the  principal  beai'ings,  as 
the    force    of   the   piston    obviously  increases    in    the    invei'se 


398  THE  STEAM-SIIIP  PBIXGETON.  chap.  xxv. 

ratio  of  tlie  shie.s  of  tLe  angles  of  tlie  pistou-sluift  cninks, 
with  reference  to  the  position  of  the  conneoting-rod.  A  very 
moderate  increase  of  diameter  makes  up  tlie  h)ss  consequent 
on  the  sliort  arc  tliroiigh  A\]iich  the  piston  ^'ibrates.  Very 
deep  cylinder-covers,  giving  great  strength  tti  resist  the  u[)- 
ward  pressure  of  the  steam,  may  also  l)e  named  as  an  advan- 
tage i-esulting  from  the  shoi't  viljration. 

"xVs  an  instrument  of  producing.  In'  dii-ed  means,  the 
high  speed  requisite  for  screw-propellers,  this  engine  com- 
mends itself  to  the  engineer.  In  its  fitness  for  screw-vessels 
it  seems  to  fulfil  every  condition.  The  very  limited  number 
of  woi-kiug  parts,  and  the  small  amount  of  matter  to  be  kept 
in  motion,  are  self-evident  advantages,  best  understood  by 
reference  to  the  plate.  It  is  important  to  notice  that  the 
pistou-shaft  journals  are  supported  by  bearings  placed  out- 
.side  of  the  heads  of  the  semi-eylinders,  and  that  the  brasses 
admit  of  adjustment  in  every  direction  ;  the  exact  position  of 
the  centre  of  the  piston-shafts,  -with  relati(jn  to  the  centre  of 
the  semi-cylinders,  being  indicated  by  an  external  index, 
enabling  the  engineer  at  all  times  to  keep  the  shaft  in  line. 

"The  main  packing  is  rendered  accessible  by  lifting  up 
one  of  the  covers  and  removing  the  nearest  side-plate  form- 
ing the  packing-groove.  The  upper  packing  becomes  acces- 
sil)le  by  lifting  up  the  centre-piece  whicli  forms  the  ujiper 
semi-cylinder.  It  may  be  stated  with  regard  to  tlie  packings, 
that  the  Prineetoi),  after  having  served  during  the  war  with 
Mexico,  was  desj^atched  on  a  ci'uise  to  the  Mediterranean 
without  recpiiring  new  packings." 


cu.vr.  XXV.  TUB  STEAM-SHir  I'L'IXCETON.  399 

Mr.  J.  O.  Siuyvnt,  iu  ii  lectui'e  on  "  Steam  Navigation  and 
the  Arts  of  Naval  Warfare,"  delivered  before  the  Boston 
Lyceum  in  1844,  stated  with  reference  to  the  motive  power 
of  the  Princeton  :  "  The  next  peculiarity  to  be  noticed  in 
tlie  Princeton  is  the  absence  of  the  ordinary  tall  smoke-pipe 
employed  to  pi-oduce  the  draught  for  keeping  up  combustion 
in  the  furnaces  of  the  boilers.  The  smoke-pipe  has  hitherto 
formed  a  serious  objection  to  a  steamer  as  a  ship-of-w  ar ;  for 
the  moment  it  is  carried  away  the  efficiency  of  the  engines 
ceases  from  want  of  steam.  The  draught  in  the  boilers  of 
tlie  Princeton  is  promoted  by  means  of  blowois  plat-ed  in 
the  bottom  of  the  vessel,  and  is  cpiite  independent  of  the 
lieigJtt  of  the  smoke-pipe,  wliich  is  only  carried  about  five 
feet  above  the  deck  of  the  ship.  If  this  inconsiderable  pro- 
jection should  become  partially  deranged  by  a  sliot,  the 
(h-aught  kept  up  by  tlie  Ijlowers  will  continue  as  efficient 
as  before. 

"  It  is  not  out  of  place  here  to  observe  that  Ericsson  was 
the  first  to  apjily  to  marine  engines  centrifugal  blowers,  now 
so  common  in  this  country  in  all  boilers  using  anthracite 
coal.  In  the  year  IS.'H  he  ai)plied  such  a  blower,  worked 
by  a  separa^te  small  stcaiii-engiiic,  to  the  steani-packct  i'orsdir, 
of  one  hundi'ed  and  twenty  liorse-powej',  plying  between 
Liverpool   and    Belfast." 


CHAPTER   XXYI. 

TWELVE-INCH  WEOUGHT-IEON  GUN  AND   CARRIAGE. 

(SEE   PLATE   41.) 


The  question  has  frequently  been  asked,  When  was 
VTi'ought-iron  orcluauce  first  introduced  on  board  ships-of-war  ? 
When  was  breeching  first  disjiensed  with  and  wrought-iron 
carriages  introduced  ?  The  heading  on  the  plate  referred  to 
gives  an  answer  to  these  queries. 

Captain  Robert  F.  Stockton,  of  the  United  States  Navy, 
on  visiting  England — 1839 — for  the  purpose  of  witnessing  the 
trial  of  a  small  screw-steamer  (the  first  iron  vessel  to  cross 
the  Atlantic)  built  for  him  by  Messrs.  Laird,  to  my  design, 
consulted  me  regarding  the  possibility  of  constructing  naval 
ordnance  of  wrouo;ht  iron.  Beinar  an  advocate  of  that  mate- 
rial,  I  readily  met  the  wishes  of  Captain  Stockton,  and  at 
once  prepared  drawings  of  a  gun  of  12-inch  calibre.  The 
Mersey  Iron-Works,  near  Liverpool,  being  willing  to  enter 
into   a   contract   with   Captain   Stockton,   received   forthwith 


cuAi'.  XXVI.       ]yi!()iaiiT-n;o.\  auxs  axd  caiuhaoks.  401 

an  order  from  that  euterprisiug  and  spirited  officer  to  build 
the  gun  at  his  expense.  Experienced  commodores  at  the 
time  protested  loudly  against  the  proposition  to  mount  "the 
monster  gnu "  on  board  a  vessel  so  lightly  built  as  tlit* 
Princeton,  insisting  tliat,  among  other  difficulties,  the  breech- 
ing Avould  tear  her  upper  works  to  pieces.  It  was  Urged 
by  the  opponents  of  my  new  system  that  the  handling  of 
such  guns  at  sea  would  prove  impossible,  the  constructing 
carriages  of  sufficient  strength  being  pointed  out  as  imprac- 
ticable; while  the  imprudence  on  the  part  of  the  Navy 
Department  of  entrusting  such  matters  to  mere  engineer- 
ing skill  was  severely  criticised.  In  spite  of  remonstrances, 
however,  Captain  Stockton's  influence  with  the  Govei-nment 
prevailed.  In  the  meantime  the  problem  of  handling  the 
12-incli  gun  received  due  attention.  Calculations  of  the 
dynamic  equivalent  of  the  recoil  convinced  me  that  a  mode- 
rate resistance,  if  continuous  and  uniform,  would  suffice  to 
bring  the  piece  to  rest  in  less  space  than  that  required  by 
breeching.  Friction,  being  the  simplest  means  of  obtaining 
a  continuous  resistance,  was  accordingly  resorted  to.  The. 
method  adopted  will  be  readily  comprehended  by  reference 
to  the  illustration  already  referred  to,  which  represents  a  side 
elevation,  top  view,  and  imuI  views  of  the  gun,  carriage,  and 
slide,  mounted  on  board  the  Princeton  in  1843.  Two  pieces 
of  timber  of  semi-circular  section,  placed  a  few  inches  apart, 
slightly  taper  towards  the  front  end  of  the  slide,  are  secured 
to  the  latter  in  such  a  manner  as  to  admit  of  some  vertical 
motion.      A  broad   hoop  of  plate-iron,  attached  to   the   car- 


402  WEOUGET-IBOX  GUNS  AND  CABEIAGES.        chap.  xxvi. 

riage,  clasps  the  two  timbers.  An  axle  pi'ovided  with  a  cam 
in  the  middle,  operated  by  a  lever,  is  placed  across  the  front 
end  of  the  slide  passing  through  the  space  between  the  fric- 
tion timbers.  Obviously,  these  timbers  will  be  pushed  apart 
with  considerable  force  if  the  transverse  axle  be  turned  so 
as  to  place  the  cam  in  a  vertical  position.  The  friction  be- 
tween the  hoop  and  the  timbers  produced  by  the  pressure 
of  the  cam,  it  is  scarcely  necessary  to  observe,  "will  be  greatly 
enhanced  during  the  recoil  of  the  gun,  in  consequence  of  the 
increasing  vertical  depth  of  the  timbers  towards  the  rear 
end  of  the  slide.  The  transverse  axle  being  turned  so  as  to 
place  the  cam  in  a  horizontal  position,  permitting  the  friction 
timbers  to  approach  each  other,  will  of  course  at  once  relieve 
the  friction.  The  monitor  gun-carriages,  constructed,  like  the 
Princeton''s,  on  the  plan  of  checking  the  recoil  by  friction, 
differed  as  regards  the  mode  of  clasping  the  friction-timbers, 
a  screw  being  employed  to  produce  the  requisite  compres- 
sion in  place  of  the  transverse  axle  and  its  cam.  But  in 
constructing  gun-carriages  for  the  celebrated  thirty  Spanish 
gunboats,  and  in  all  recent  carriages,  I  have  returned  to 
the  plan  of  employing  a  cam  for  setting  up  and  relieving 
the  friction,  whereby,  as  in  the  case  of  the  Princeton  car- 
riage, the  operation  becomes  almost  instantaneous. 

The  12-in.  Avronght-iron  gun  of  the  Princeton,  as  stated, 
was  manufactured  at  the  Mersey  Iron-AVorks,  of  the  very 
best  materials,  it  has  been  asserted;  but,  on  being  tested  in 
this  country,  it  proved  too  weak.  I  therefore  resorted  to 
the  expedient  of  hooping  the  breech  of  the  piece  up  to  the 


CUAP.  XXVI.         WBOUGHT-II;OX  GUXS  AND  CARI^IAGES.  403 

truunion-band ;  the  hoops  beiug  made  of  the  best  quality 
of  American  wrought-irou  put  on  in  two  tiei-s,  shrunk  one 
over  the  other  in  such  a  manner  as  to  break  joint.  This 
expedient  proved  entirely  successful,  the  gun  having  stood 
all  tests  to  which  it  has  been  subjected.  It  was  a  solid 
cast-iron  shot  from  this  12-in.  gun  which  in  1842  pierced  a 
wrought-iron  target  4^  ins.  thick,  up  to  that  period  considered 
proof  against  naval  ordnance. 

The  United  States  Government  having  been  the  firat  to 
introduce  heavy  MTought-iron  ordnance  for  naval  purposes, 
why  does  it  not  continue  to  build  guns  of  that  material  ? 
European  artillerists  repeatedly  jnit  this  question.  Probably 
the  answer  will  be  found  in  the  fact  that,  although  having 
in  the  meantime  successfully  constructed  rifled  wi-ought-iron 
ordnance  of  considerable  size,  the  first  essay  at  buildiuo- 
heavy  guns  for  naval  purposes  proved  most  disastrous.  Im- 
mediately after  the  trial  of  the  gun  referred  to,  manufactured 
in  England,  a  12-in.  smooth-bore,  of  much  heavier  metal,  was 
forged  at  Hamersley  Forge,  bored  and  turned  in  New  York, . 
and  considered  at  the  time  to  be  a  remarkable  specimen  of 
good  workmanship.  It  was  at  once  mounted  on  board  the 
Princeton,  by  the  side  of  its  slender  companion,  upon  a  similar 
carriage.  Much  confidence  was  placed  in  the  strength  of  this 
magnificent  gun  on  account  of  the  supposed  superior  quality 
of  American  iron.  It  stood  the  proof-charge  and  some  preli- 
minaiy  tests,  but,  on  being  fired  on  a  festive  occasion  while 
the  ship  was  at  Washington,  the  admired  piece  burst,  Avith 
the  sad  result  recorded  in  the  naval  annals  of  the  time. 


CHAPTER  XXVII. 

APPLICATION   OF   THE   SUBMEEGED    PEOPELLER   FOI!   COM- 
MERCIAL PURPOSES. 


Dttking  tlie  constniction  of  the  Princeton  numerous  pro- 
peller-vessels were  built  for  carrying  freight  on  the  rivers 
and  inland  waters  of  the  country,  the  machinery  at  first  being 
built  in  New  York,  Philadelphia,  and  Oswego.  The  line  of 
propeller-steamers  between  Philadelphia  and  Baltimore,  which 
seriously  interfered  with  the  freight  traffic  of  the  Philadel- 
phia and  Baltimore  Eailroad,  merits  special  mention. 

The  annexed  table  of  propeller-vessels  built  up  to  Decem- 
ber, 1843,  prepared  by  Lieutenant  Johnson,  of  the  Swedish 
Navy,  in  pursuance  of  orders  from  his  Government,  shows 
the  extraordinary  rapidity  of  the  adoption  of  the  propeller 
for  commei'cial  purposes. 

The  Migineer,  in  laying  the  table  referred  to  before  its 
readers.  May  11,  1866,  observes: 

"The  fate  of  mechanical  inventions  is  much  like  that  of 


CHAP.  XXVII.        SCREW  PROPULSION  AKD  COMMERCE.  405 

tlie  seed  in  the  parable.  Tlie  Invention  must  fall  on  a  pro- 
per soil,  and  be  nurtured  by  favorable  circumstances  of  time 
and  place,  in  order  to  bloom  into  success.  The  application 
of  the  steam-engine  to  navigation  was  of  greater  necessity 
to  the  large  e.xteut  of  the  rivers  and  lakes  of  the  States  than 
\vith  oui-selves ;  and  Fulton  did  right  to  take  his  marine 
engine  back  to  his  own  country.  For  similar  reasons  the 
screw-propeller  worked  its  way  into  use  there  much  quicker 
than  with  ourselves.  This  fact  is  very  evident  from  the 
table  furnished  to  Mr.  Woodcroft  by  Captain  Ericsson,  pre- 
pared by  Lieutenant  Johnson,  of  the  Swedish  Navy,  in  1843. 
Early  in  the  following  year  (1844)  a  very  large  addition 
was  made  to  the  steam  fleet  provided  with  Ericsson's  pro- 
peller both  on  the  inland  waters  of  America  and  on  the 
ocean.  Of  the  latter  may  be  mentioned  the  bark  Bdifh  and 
the  steamshi^w  JlcICim,  Marmora,  and  Mamachusetts.  The 
last  vessel  was  subsequently  purchased  by  the  United  States 
Government.  It  became  the  flag-ship  of  General  Scott  at 
the  landing  of  Vera  Cruz,  which  lesulted  in  the  conquest 
of  Mexico.  It  is  woi-thy  of  notice  that  Ericsson  applied  his 
propeller  to  upwards  of  sixty  vessels  in  America  before  any 
other  form  of  propeller  was  adopted  or  a  single  attempt  made 
at  evading  his  patent.  Nor  is  it  less  worthy  of  remark  that 
the  adaptation  of  his  pi'opeller  proved  a  great  commercial 
success  from  the  start,  many  of  the  original  vessels  being 
now,  after  fifteen  years  of  service,  in  good  working  condi- 
tion." 


406 


SCBEW  PllOPULSION  AND  COMMERCE. 


CHAP.   XXVII. 


List  of  Steam  Vessels  in  North  America  provided  with 
Ericssox's  Screw-Propeller  up  to  December,  1843. 

Names  of  the  vessels. 

Destination. 

Robert  F.  Stockton 

Vandalia           

Delaware  and  Schuylkill 

Oswego  to  Chicago 

2 
2 
1 
1 
2 

2 
2 
2 
2 

Clarion 

New  York  to  Havana 

Baron  Toranto 

Rideau  Canal  and  St.  Lawrence. 
Rideau  Canal  and  St.  Lawrence. 
Rideau  Canal  and  St.  Lawrence. 
Rideau  Canal  and  St.  Lawrence. 

Philadelphia  to  Albany 

Philadelphia  to  Albany 

Philadelphia  to  Hartford 

Pliiladelphia  to  Hartford 

Erie  Canal 

Royal  Barge 

Propeller 

Ericsson 

Ironside 

Anthracite 

Black  Diamond 

Vnlcan 

Pioneer 

Oswego 

Oswego  to  Chicago 

Chicago 

Osw^ego  to  Chicago 

Cumberland 

Philadelphia  to  Baltimore 

Philadelphia  to  Baltimore 

New  York  to  Canada 

Ericsson 

Pilot      

Phcenix 

New  York  to  Canada 

Governor  McDowell 

Jefferson  (Revenue  Cutter) 
Legare 

James  River  Canal  to  Virginia. 
Lake  Erie 

Delaware  River 

CHAP,  xxvii.       SCJii:W  rEOPULSIOX  asd  commeece. 


407 


3 

4 
5 
6 

7 
8 

9 

10 

II 

12 

13 
14 
15 
i6 

17 
i8 

19 
20 
21 


List  of  Steam  Vessels  in  Xortii  Ameuica  puovided  with 
Ericsson's  Screw-Phopelleu  up  to  December,  1843. 


60 
40 
60 
18 
36 
18 
18 
40 
40 
40 
40 
18 
40 
40 
40 
40 
18 
18 
IS 
150 
150 


42 

140 

250 

70 

70 

70 

70 

200 

200 

200 

200 

55 

140 

140 

80 

80 

55 

55 

20 

342 

342 


Ft. 

70 

98 

104 

72 

72 

72 

72 

100 

100 

100 

100 

82 

98 

98 

78 

78 

82 

82 

90 

140 

140 


Ft.  In. 

10  0 

21  6 
24  6 
16  6 
16  6 
16  6 
16  6 

22  6 
22  6 
22  6 
22  6 
14  4 
21  6 
21  6 
18  6 
18  6 
13  6 
13  6 
13  6 
24  0 
24  0 


Ft.  In. 

7  0 

6  6 

13  0 

4  6 

4  6 

4  6 

4  6 

6  0 

6  0 

6  0 

6  0 

3  6 

6  6 

6  6 

6  6 

6  6 

3  6 
3 
1 
7 
7 


9 

5  9 

5  9 

6  0 
6  0 
6  0 
6  0 
5  6 


5 

9 

5 

9 

6 

6 

G 

6 

5 

6 

5 

6 

5 

0 

9 

6 

9 

6 

1839 
1841 


1842 


1843 


408 


SCREW  PliOPULSIOX  AND  COMMERCE.        chap,  xxvii. 


List  of  Steam  Vessels  in  North  America  provided  with 
Ericsson's  Screw-Propeller  up  to  December,  1843. 


Names  of  the  vessels. 


Destination. 


Hercules 

Perry  sboroiioii 

Cleveland 

Baltimore 

Priuceton 

Lion 

Eagle 

Mohawk 

C.  Bristol 

New  London 

Uncas 

IVew  London 

Enterprise 

New  York 

Washington 

Rufus  Page,  Owner. . . . 
Riifus  Page,  Owner . . . . 

Buck,  Owner 

Captain  Sanford,  Owner 

Williams  &  Barns 

Captain  Coit 


Lake  Erie 

Lake  Erie 

Lake  Erie 

PMladelphia  to  Baltimore 

Philadelpliia  Station 

New  York  to  Hartford 

New  York  to  Hartford 

Albany  to  Hartford 

Chicago  and  the  Great  Lakes. . 

Mobile 

Mobile 

Owners,  Wdliams  &  Barns . . . . 
Lake  Ontario  and  St.  Lawrence. 

Oswego  to  Chicago 

Hudson  River 

East  Coast  of  America 

East  Coast  of  America 

East  Coast  of  America 

East  Coast  of  America 

East  Coast  of  America 

East  Coast  of  America 


2 

22 

2 

23 

1 

24 

1 

25 

2 

26 

1 

27 

1 

28 

1 

29 

1 

30 

1 

31 

1 

32 

2 

33 

1 

34 

2 

35 

1 

36 

1 

37 

1 

38 

2 

39 

2 

40 

2 

41 

2 

42 

CHAP.  XXVII.      scnEW  rBoFULswy  and  commerce. 


409 


List  of  Ste.vm  Vessels  ix  North  Amkrica  provided  with 
Ericsson's  Sckew-Propellek  up  to  December,  1843. 


1 

i 

t: 

.a 

i 

2 

0 

0. 

1 

a 
.3 

1 

3 

.a 

J 

/K. 

rt.     In 

ft.     In. 

rt.     In. 

22 

60 

250 

8  0 

6  0 

1843 

23 

50 

250 

8  0 

6  0 

24 

60 

280 

8  0 

6  10 

25 

50 

127 

78 

19  6 

6  6 

7  2 

26 

400 

672 

164 

30  0 

17  6 

14  0 

27 

60 

172 

115 

23  6 

6  0 

6  10 

28 

50 

172 

115 

23  6 

6  0 

6  10 

29 

50 

172 

125 

22  0 

6  0 

7  0 

" 

30 

60 

300 

... 

26  0 

8  0 

7  4 

31 

50 

172 

125 

22  0 

6  0 

7  0 

32 

50 

172 

125 

22  0 

6  0 

7  0 

33 

50 

172 

125 

22  0 

6  6 

7  0 

34 

20 

70 

5  9 

35 

50 

140 

98 

21  6 

6  6 

5  9 

36 

00 

170 

103 

26  0 

7  6 

7  4 

37 

50 

172 

115 

23  6 

6  0 

6  10 

38 

50 

172 

115 

23  6 

6  0 

6  10 

39 

55 

172 

125 

22  0 

6  0 

7  0 

40 

55 

172 

125 

22  0 

6  0 

7  0 

41 

56 

172 

125 

22  0 

6  0 

7  0 

42 

55 

172 

125 

22  0 

6  0 

7  0 

CHAPTER    XXVIII. 


IRON-CLAD    STEAM    BATTERY,    WITH    REVOLVING    CUPOLA, 
SUBMITTED  TO   EMPEROR  NAPOLEON  III. 

(ILLUSTRATION,    SEE   PLATE   42.) 


The  illustration  referred  to  is  a  ■  f ac-simile  of  a  drawing 
forwarded  to  the  Frencli  Emperor  at  Paris,  September  26, 
1854,  accompanied  by  an  elaborate  description  and  demon- 
stration of  tlie  utility  of  the  battery.* 

The  following  extracts  from  the  description  of  the  new 
system  of  naval  attack,  forwarded  as  stated,  furnishes  a  cor- 
i-ect  idea  of  its  nature  : 

The  present  system  of  long  range  is  abortive.  1st,  because 
large  or  heavy  bodies  cannot  be  projected  to  a  great  distance  ; 

*  The  Emperor  promptly  acknowledged  the  receipt  of  these  documents  through 
Gen.  Fave,  whose  letter  commences  with  the  following  flattering  sentence  : 

"  L'Empereur  a  examine  lui-meme  aveo  le  plus  grand  soin  le  nouveaii  sysdeme 
d'attaque  navale  que  vous  lui  avez  communiqm'. 

"  S.  M.  me  charge  d'avoir  I'honneur  de  vous  informer  qu'elle  a  trouve  vos  idees 
tres-ingenieuses  et  dignes  du  nome  celebre  de  leur  auteur." 


CHAi'.  xxviJi.  HEVOLVIXG   CUPOLA  VESSEL.  411 

2dly,  because  accurate  aim  at  long  range  becomes  absolutely 
imi>ossible  in  practice.  The  recent  trial  of  the  Lancaster 
gun,  when  subjected  to  the  unavoidable  oscillation  of  a 
small  vessel,  may  be  cited  as  proof.  Short  range,  "  close 
quarters,"  will  remove  both  difliculties,  as  it  admits  of  lai'ge 
and  heavy  projectiles  being  employed,  and  because  it  ensures 
accurate  aim.  Besides  these  advantages,  a  near  approach  to 
the  enemy  renders  attack  under  water  practicable.  These 
facts  establish  the  following  propositions :  1st,  a  complete 
system  of  naval  attach  demands  a  self-moving  vessel  capable 
of  passing  witliiii  range  of  guns  of  forts,  and  of  moving  at 
pleasure  in  defiance  of  the  fire  of  broadsides.  2dly,  with  a 
vessel  of  such  properties,  a  complete  offensive  system  further 
requires  adequate  means  of  throwing  projectiles  of  large  size 
with  absolute  precision  at  short  ranges,  either  point-blank 
or  at  very  great  elevation ;  the  means  of  projecting  shells 
(movable  torpedoes)  under  water  at  short  distances  being 
also  indispensable.  3dly.  These  conditions  being  fulHlled,  the 
system  yet  demands  a  projectile  that  will  infallibly  explode 
at  the  instant  of  contact. 

Accordingly,  the  writer  has  directed  his  e.xperiments  and 
laboi-s  to  the  solution  of  the  following  problems:  I.  A  self- 
moving  shot-proof  vessel.  II.  An  instrument  capable  of 
projecting  very  large  shells  at  slow  velocities,  but  very  accu- 
rately, in  accordance  with  previously-determined  rate.  III. 
A  shell  not  subject  to  any  rotation  in  the  direction  of  its 
course,  and  so  contrived  as  to  explode  with  infallible  cer- 
tainty   at   the    instant    of    contact.       IV.    A    sliell    (toipedo) 


412  EEVOLVING  CUPOLA   VESSEL.  chap,  xxviii. 

capable  of  being  projected  under  water,  and  certain  to  ex- 
plode by  contact,  together  witb  an  instrument  for  projecting 
sucli  a  shell  from  the  vessel  at  a  certain  depth  below  the 
water-line. 

The  nature  of  the  practical  solution  of  the  above  prob- 
lems will  be  readily  comprehended  by  referring  to  the  illus- 
trations (see  Plate  42).  A  brief  extract  of  the  document 
forwarded  to  the  Emperor  will  therefore  suffice. 

The  vessel  to  be  composed  entirely  of  iron.  The  mid- 
ship section  is  triangular,  with  a  broad,  hollow  keel,  loaded 
with  about  200  tons  of  cast-iron  blocks  to  balance  the 
heavy  upper  works.  The  ends  of  the  vessel  are  moderately 
sharp.  The  deck,  made  of  plate  iron,  is  curved  both  longi- 
tudinally and  transversely,  the  curvature  being  5  feet ;  it  is 
made  to  project  8  feet  over  the  rudder  and  propeller.  The 
entire  deck  is  covered  with  a  lining  of  sheet  iron  3  inches 
thick,  with  an  opening  in  the  centre  16  feet  diameter.  Over 
this  opening  is  placed  a  semi-globular  turret  of  plate  iron 
6  Inches  thick,  revolving  on  a  vertical  column  by  means  of 
steam-po^ver  and  appropriate  gear-"\voi'k.  The  vessel  is  pro- 
pelled by  a  powerful  steam-engine  and  screw-propeller.  Air 
for  the  combustion  in  the  boilers  and  for  ventilation  within 
the  vessel  is  supplied  by  a  large  self-acting  centrifugal 
blower,  the  fresh  air  being  drawn  in  through  numerous 
small  holes  in  the  turret.  The  products  of  combustion  in 
the  boilers  and  the  impure  air  from  the  vessel  are  forced  out 
through  conductors  leading  to  a  cluster  of  small  holes  in 
the  deck  and  tiUTet.     Surrounding  objects  are  viewed  through 


CHAP.  XXVIII.  REVOLVING  CUPOLA   VESSEL.  413 

small  perforations  at  appropriate  places.  Reflecting  telescopes, 
capable  of  being  pi-otriuled  or  witbtlrawn  at  pleasure,  also 
afford  a  distinct  view  of  surrounding  objects.  The  rudder- 
stock  passes  tbrougb  a  water-tigbt  stufliug-box,  so  as  to  admit 
of  the  helm  being  worked  within  the  vessel.  Shot  striking 
the  deck  are  deflected,  whilst  shell  exploding  on  it  will 
prove  harmless. 

Tube  for  projecting  the  shells  to  be  made  of  cast  iron 
or  brass,  20  inches  bore,  2  inches  thick,  and  10  feet  long. 
It  is  ojien  at  one  end,  the  other  end  being  closed  by  a 
door  moving  on  hinges  provided  with  a  cross-bar  and  set- 
screw,  in  order  to  be  quickly  opened  and  afterwards  fli-mly 
secured.  The  shell  is  inserted  through  this  door,  and  pro- 
jected by  the  direct  action  of  steam  admitted  from  the  boiler 
of  the  vessel  through  a  large  opening  at  the  breech.  The 
induction-valve  is  made  with  a  double  face  of  large  areas, 
and  moved  by  mechanism  of  instantaneous  action,  susceptible 
of  accurate  regulation  in  regard  to  opening.  One  tube  of 
the  above  description  is  placed  on  a  level  on  the  platfonn 
of  the  revolving  tun-et.  Two  similar  tubes  are  placed  in 
the  body  of  the  vessel,  at  a  fixed  inclination  of  22  deg., 
revolving  on  vertical  pivots.  These  tubes  are  supplied  with 
steam  through  the  centre  of  their  vertical  pivots,  the  admis- 
sion of  steam  being  regulated  as  before  described. 

The  plan  of  throwing  shells  of  several  hundred  pounds 
by  the  direct  power  of  steam  of  ordinary  pressure,  demands 
special  notice.  Without  reference  to  the  result  of  actual 
trial,  a  brief  investigation  of  the  theoiy  on  which  the  plan 


414  BEVOLVINQ  CUPOLA  VESSEL.  chap,  xxviii. 

is  based  will  show  that  shells  of  enormous  size  may  be  pro- 
jected with  uuerriug  precision. 

The  Shell,  composed  of  cast  iron,  is  formed  as  delineated.* 
A  groove  is  made  round  the  circumference  at  right  angles 
to  the  axis,  into  which  an  india-rubber  ring  is  inserted  to 
form  a  steam-tight  joint  when  the  shell  is  put  into  the  tube. 
In  order  effectually  to  prevent  rotation  in  the  line  of  flight, 
a  tail  in  the  form  of  a  cross,  composed  of  thin  plate-iron,  is 
attached  to  the  shell.  Opposite  to  this  tail  a  cavity  is 
formed,  into  which  a  cylindrical  hammer  is  inserted.  A 
peroussion-wafer  is  placed  under  the  hammer,  which,  being 
always  in  advance  of  the  shell,  is  struck  at  the  instant  of 
contact,  infallibly  causing  an  explosion. 

The  Hydrostatic  Javelin  (torpedo-carrier),  for  convey- 
ing the  shell  (torpedo)  under  water,  consists  of  a  cylindrical 
block  of  light  wood,  16  inches  diameter,  10  feet  long.  At 
one  end  of  this  block  a  16-inch  shell  is  attached,  charged 
■with  powder,  and  furnished  with  a  percussion-hammer,  as 
above  described.  The  other  end  of  the  block  is  pointed  and 
loaded  at  the  under-side  sufficient  to  balance  the  instrument 
perfectly.  The  displacement  being  1,000  pounds,  the  weight 
of  the  whole  is  made  to  correspond  accurately,  in  order  to 
ensure  perfect  suspension  in  the  water.  The  javelin  (torpedo- 
carrier),  when  required,  is  passed  through  the  vessel's  bow 
or  side  by  means  of  a  short  tube,  as  shown  by  the  drawing, 
the  water  from  the  sea  being  kept  out  during  the  insertion 

*  Unfortunately,  the  copies  of  this  and  other  delineations  referred  to  have  been  lost, 
henc3  cannot  be  presented  in  this  work. 


CHAP,  xxviii.  BEVOLVIXQ  CUPOLA  VESSEL  416 

by  the  obvious  means  of  a  slide-valve.  The  javelin  (torpedo- 
carrier)  is  projected — pushed  out — by  means  of  a  rod  attached 
to  the  piston  of  a  steam-cylinder  of  18  inches  diameter,  3  feet 
stroke.  A  force  of  10,000  pounds  acting  through  3  feet  is 
more  than  sufficient  to  propel  the  javelin  200  feet,  at  an 
average  velocity  of  12  feet  per  second.  The  javelin  (torpedo- 
carrier)  is  readily  kept  at  any  particular  depth  during  its 
progress  by  a  simple  application  of  the  hydrostatic  pressure 
on  a  tail  or  radder  acting  in  the  horizontal  plane.  The  load 
inserted  at  the  tail  end  of  the  javelin  (torpedo-conductor) 
to  balance  the  shell  (torpedo)  being  applied  at  the  bottom, 
the  instrument  cannot  turn  in  the  water. 

CONCLUDING    REMARKS. 

This  new  system  of  naval  attack  will  place  an  entire 
fleet  of  sailing  vessels,  during  calms  and  light  winds,  at  the 
mercy  of  a  single  craft.  "Boarding"  as  a  means  of  defence 
will  be  impracticable,  since  the  turret  guns,  which  turn  like 
the  spokes  in  a  wheel,  commanding  every  point  of  the  com- 
pass at  once,  may  keep  off  and  destroy  any  number  of  boats 
by  firing  slugs  and  combustibles.  The  loading  at  the  breech 
and  the  dispensing  Avith  sponging  ensures  a  rapidity  in  the 
discharge  of  missiles  quite  irresistible  in  an  attempt  at 
boarding.  A  fleet  at  anchor  might  be  fired  and  put  in  a 
sinking  condition  before  being  able  to  get  under  way. 

Of  what  avail  would  be  the  "  steam  guard-ships  "  if  at- 
tacked on  the  new  system  ?  Alas  !  for  the  "  wooden  walls  " 
that  formerly  "ruled  the  waves."  The  long-range  Lancaster 
gun   would   scarcely   hit   the   revolving   iron   turret   once   in 


416  BEVOLYING   CUPOLA    VESSEL.  chap,  xxviii. 

six  hours,  and  tlieii,  six  cliances  to  one,  its  shot  or  shell 
Avould  be  deflected  hy  the  varying  angles  of  the  face  of  the 
impregnable  globe.  When  ultimately  struck  at  I'ight  angles, 
the  globe,  which  weighs  upwards  of  40  tons,  Avill  be  less 
affected  by  the  shock  than  a  heavy  anvil  by  the  blow  of 
a  hammer.  Cousequentl}',  a  cast-iron  shot  would  crumble 
to  pieces,  whilst  an  exploding  shell  would  strew  the  arched 
deck  with  harmless  fragments. 

During  contest  the  revolving  turret  should  be  kept  in 
motion,  the  port-holes  being  turned  away  from  the  opponent 
except  at  the  moment  of  discharge,  which,  however,  should 
be  made  during  full  rotation,  as  the  lateral  aim  in  close 
quarters  requires  Ijut  little  precision.*'" 

*  Captain  Coles,  of  the  British  Navy,  having  claimed  priority  of  invention,  the 
following  statement  was  published  in  various  nautical  and  mechanical  journals  (1863) : 

"  Absurdity  of  Captain  Coles's  Claim. — Captain  Coles  states,  in  a  letter  to  the 
Times  of  April  5,  1863,  that  his  experience  in  the  Baltic  and  Black  Seas,  in  1855, 
suggested  to  him  the  idea  of  buUding  impregnable  vessels,  and  that,  towards  the 
latter  part  of  that  year,  he  had  '  a  rough  model  made  by  the  carpenter  of  the  Strom- 
boli,'  and  that  he  ])roposed  to  protect  the  guns  by  a  stationary  shield  or  cupola. 
Captain  Coles,  it  appears,  met  with  no  encouragement  from  the  Admiralty,  and  there- 
fore consulted  Mr.  Brunei,  the  celebrated  engineer,  who  warmly  embraced  the  plan. 
'  He  did  more,'  says  Captain  Coles  in  his  letter  to  the  Times :  '  he  assisted  me  in  my 
calculations,  and  gave  me  the  aid  of  his  draughtsmen.'  Captain  Coles  further  states 
that,  notwithstanding  oflficial  neglect,  he  persevered,  and  in  March,  1859,  produced 
drawings  of  a  '  shield  fitted  with  turn-tables.'  Lastly,  in  December,  1860,  Captain 
Coles  published  in  Blachvood's  Ilagazine  drawings  of  his  '  gun-shield  and  revolving 
platform,'  the  platform  being  turned  by  manual  power  only." 


CHAPTER   XXIX. 


SURFACE-CONDENSER,  OPERATED  BY  INDEPENDENT  STEAM- 
POWER. 

(SEE   PLATE   43.) 


The  following  is  an  exact  copy  of  the  description  accom- 
panpng  the  patent  granted  by  the  United  States  (1849)  for 
the  independent-action  condenser  illustrated  on  the  plate  re- 
ferred to : 

Fig.  1  is  a  longitudinal  vertical  section ;  Fig.  2,  a  cross- 
section  of  the  condenser  taken  at  the  line  (X  X)  of  Fi<y.  1; 
and  Fig.  3,  a  cross-section  of  the  pumping  part  of  the  appa- 
ratus and  the  auxiliary  engine  by  which  it  is  operated.  The 
same  letters  indicate  like  i^arts  in  all  tlie  figiu-es. 

The  object  of  my  invention  is  to  condense  the  steam 
without  admixture  with  the  condeusing-water,  that  the  water 
produced  by  the  condensation  may  be  carried  back  to  the 
boiler,  to  prevent  the  evil  consequences  arising  from  the  use 
of  water  that  contains  in  solution  or  suspension  mineral   or 


418  SUBFACE  CONDENSATION.  chap.  xxix. 

other  solid  matter,  and  to  condense  the  steam  which  escapes 
from  the  safety-valve,  and  also  for  the  production  of  fresh 
water  for  any  other  use. 

In  my  fresh-water  apparatus  I  use  a  tubular  condenser, 
through  the  tubes  of  which  the  steam  passes,  and  is  con- 
densed by  the  cooling  influence  of  a  current  of  cold  water 
taken  from  the  outside  of  the  vessel  or  ship,  and  made  to 
pass  outside  of  the  tubes ;  and  to  this  end  the  first  part  of 
my  invention  consists  in  combining  the  condenser  of  a  steam- 
engine  for  the  propelling  of  a  ship  or  vessel  with  a  pump 
which  receives  the  condensing  water  from  outside  the  ship  or 
other  vessel,  and  causes  it  to  pass  through  the  condenser,  the 
said  pump  being  operated,  irrespective  of  the  engine  that  pro- 
pels the  vessel,  by  means  of  an  auxiliary  engine,  whereby  the 
amount  of  condensation  can  be  regulated  independently  of  the 
working  of  the  engine  that  propels  the  vessel.  The  second 
part  of  my  invention  consists  in  connecting  the  condenser  with 
the  boiler  or  boilers,  or  any  part  thereof,  in  addition  to  its 
or  their  connection  with  the  exhaust  of  the  engine,  when  the 
pump  which  carries  the  condensing  water  through  the  con- 
denser is  operated  by  an  auxiliary  engine,  by  means  of  which 
double  connection  not  only  is  the  steam  that  escapes  from 
the  safety-valve  condensed  to  be  carried  back  to  the  boiler, 
but  the  boiler  or  boilers  may  be  used  to  distil  and  produce 
fresh  water  for  any  purpose  desired  when  the  engine  is 
not  employed  for  propelling  the  vessel.  And  the  last  part 
of  my  invention  consists  in  connecting  the  tubes  of  the  con- 
denser with  the  cylinder  or  outer  case  thereof  by  connecting 


CHAP.  XXIX.  SURFACE  CONDEKSArioy.  419 

oue  or  botli  of  the  diapliragins  to  wliicb  the  ends  of  the 
tubes  are  secured  with  the  outer  cylinder  or  case  by  means 
of  a  ring  and  flange,  or  the  equivalent  thereof,  so  that  the 
said  ring  or  flange  may  bend  to  adapt  itself  to  the  unequal 
contraction  and  expansion  of  the  tubes  and  cylinder  or  outer 
case  of  the  condenser. 

In  the  drawings  on  Plate  43  (a)  represents  a  horizon- 
tal cylinder,  within  which  are  arranged  a  series  of  small 
parallel  tubes  (h).  One  end  of  the  said  tubes  is  secured,  in 
the  usual  way  or  any  other  desired  and  appropriate  manner, 
to  a  diaphragm  (c),  which  has  a  turned  flange  through  which 
rivets  or  bolts  ('/)  pass  to  secure  it  to  the  cylinder  (a),  and 
within  such  distance  of  the '  head  as  to  leave  a  sufl5cient 
space  between  it  and  the  head  (e)  of  the  cylinder  for  two 
chambers  (/)  and  (g),  these  two  chambers  being  separated 
by  a  horizontal  diaphragm  or  partition  (h).  The  other  ends 
of  the  tubes  are  in  like  manner  secured  to  another  diaphragm 
(/)  at  the  other  end,  which  said  diaphragm,  instead  of  being 
bolted  directly  to  the  end  of  the  cylinder  in  the  usual  way, 
is  bolted  to  a  ring  (j)  near  its  outer  periphery,  the  inner 
peripheiy  thereof  being  provided  with  a  turned  flange  bolted 
to  the  end  of  the  cylinder ;  l)ut,  instead  of  this,  the  end  of 
the  cylinder  may  be  made  with  a  flange  corresponding  in 
size  and  form  with  this  ling,  and  the  diaphragm  bolted  to 
its  outer  periphery.  The  said  ring  or  flange  should  be 
slightly  conical,  or  bent,  that  the  diaphragm  may  be  at  some 
distance  from  the  end  of  the  cylinder,  that  it  may  move  in 
and  out  to  adapt  itself    to  the  unequal   contraction   and   ex- 


420  SURFACE  CONDENSATION.  chap.  xxix. 

pansiou  of  the  tubes  and  cylinder  by  reason  of  the  passage 
of  the  steam  through  the  tubes  and  the  water  for  the  con- 
densation through  the  cylinder.  A  chamber  (Jc)  is  formed 
at  this  end  of  the  cylinder  by  means  of  a  head  (/)  secured 
to  the  diaphragm  by  means  of  a  double-flanged  ring  (??;)  and 
screw-bolts,  that  it  may  be  removed  to  give  access  to  the 
tubes. 

The  upper  chamber  (/),  at  the  end  of  the  cylinder  first 
described,  communicates,  by  means  of  a  pipe  («-),  in  any  de- 
sired manner  with  the  exhaust-pipe  of  the  engine,  and,  by 
another  pipe  (/?'),  also  with  the  escape-pij^e  of  the  boiler, 
and  these  connections  shoiild  be  governed  by  appropriate 
cocks  or  valves,  so  that  either  can  be  opened  or  closed  at 
pleasure.  Either  of  these  connections  being  opened,  the 
steam  passes  into  the  chamber  (/),  thence  tlirough  tlie 
range  of  tubes  above  the  diaphragm  or  partition  (Jt)  to  the 
chamber  (Jc)  at  the  other  end,  and  thence  back  through  the 
lower  range  of  tubes  to  the  lower  chamber  (g),  which  com- 
municates by  means  of  the  pipe  (o)  with  the  air-pump  and 
supply-pumps  of  the  engine,  or,  this  connection  being  closed, 
by  means  of  a  pipe  (o')  with  any  desired  recipient  with 
which  the  pipe  (o')  may  communicate.  The  direction  of  the 
passage  of  steam,  and  the  water  produced  by  its  condensa- 
tion, through  the  tubes,  is  indicated  by  the  dotted  ai'rows. 

The  steam,  in  passing  through  the  tubes,  is  condensed  by 
the  cooling  influence  of  a  constant  current  of  cold  water 
which  passes  outside  of  the  tubes,  and  which  travels  in  a 
direction   the    reverse    of    the  current  of   steam,  as  indicated 


CHAP.  XXIX.  SrRFAC£  CONDENSATION.  421 

by  the  white  arrows,  so  that  the  steam  a.s  it  parts  with  its 
caloric  is  constantly  approaching  a  cooler  medium. 

The  water  for  the  conclensatiou  is  forced  into  the  cylinder 
(<a),  near  the  diaphragm  (c),  through  a  pi[)e  {j)),  and  passes 
around  the  lower  half  of  the  series  of  tubes  until  it  strikes 
the  other  diaphragm  (<)  ;  thence  it  passes  up  around  the  end 
of  a  horizontal  position-plate  (<2)  on  the  same  plate  (/c), 
which  plate  (q)  extends  from  the  diaphragm  (c)  to  within 
a  short  distance  of  the  othei'  diaphragm  (/),  and  from  this 
the  water  passes  around  all  the  upper  half  of  the  tubes  to 
the  firat,  where  it  escapes  at  the  top  through  a  ])ipe  (/) 
that  discharges  through  the  side  of  the  vessel  above  the 
water-line. 

The  water  from  the  condensation  is  impelled  through  the 
condenser  by  a  rotating  pump,  the  case  (s)  of  which  is  pro- 
vided with  a  tangential  pipe  {t)  at  the  lower  part  connected 
\nth  the  part  (/))  by  the  condenser.  And  this  case  is  also 
provided  with  another  pipe  ('/)  which  extends  from  the 
centre  thereof,  to  and  through  the  side  of  the  vessel,  and 
so  far  down  as  to  be  always  below  the  water-line,  that  the 
water  may  flow  through  it  to  the  inside  of  the  pump-case. 
To  the  centre  of  this  case  is  adapted  the  shaft  (^•),  the 
Journals  of  which  run  in  appropriate  boxes  («'  ir)  in  the 
case,  and  pi-ovided  with  stuffing-boxes  to  prevent  the  escape 
of  water;  and  on  this  shaft  is  a  hub  (x),  Avith  four  arms 
or  vanes  (y)  accurately  fitted  to  the  case,  and  yet  to  rotate 
without  touching  it.  By  the  rotation  of  these  arms  or  vanes 
the  water  is  drawn  in   near  the  centre,  and   by  centrifugal 


422  SUBFAVE  CONDENSATION.  chap.  xxix. 

force  carried  out  through  the  tangential  pi^^e  (;;)  to  and 
through  the  condenser.  And  the  required  rotation  of  the 
pump  is  given  by  an  engine  («')  secured  to  the  casing  of 
the  rotary  pump  as  represented  in  the  drawings,  and  the 
connecting-rod  (h'),  which  is  jointed  in  the  usual  manner  to 
the  cross-head  {c'),  takes  hold  of  a  crank  (J')  on  the  shaft 
of  the  pump,  the  said  shaft  being,  in  the  usual  manner,  pro- 
vided with  an  eccentric  (e')  for  working  the  valves  of  the 
engine  (a'),  which  are  not  represented,  as  they  may  be  on 
any  of  the  known  plans.  The  water-supply  pump,  which 
receives  the  water  from  outside  the  vessel,  and  which  is  for 
that  purpose  l)elow  the  water-line,  is  provided  ^vith  a  valve 
(/'),  the  stem  (y')  of  which  passes  through  stuffing-boxes, 
and  has  a  handle  (/i')  by  means  of  which  the  pipe  can  be 
closed  at  pleasure  when  it  becomes  necessary  to  give  access 
to  the  inside  of  the  pump. 

From  the  foregoing  it  will  be  seen  that,  by  means  of  the 
auxiliary  engine  which  operates  the  pump,  a  constant  current 
of  cold  water  is  carried  through  the  condenser  independently 
of  the  working  of  the  propelling  engine  of  the  vessel,  and, 
as  a  necessary  consequence,  the  more  the  propelling  engine 
labors,  by  reason  of  head  winds  or  rough  watei-,  the  more 
perfect  will  be  the  condensation  and  the  vacuum  thereby 
produced,  thus  Increasing  the  power  of  the  propelling  engine 
when  the  power  is  most  needed;  whereas  if  the  current  of 
cold  Avater  were  dependent  on  the  working  of  the  proj)elling 
engine,  the  sum  of  the  mass  of  water  passing  thi'ough  the 
condenser  would  be  exactly  in  j)i'oportion  to  the  motion  of 


CHAP.  XXIX.  SURFACE  CONDENSATION.  423 

the  engine,  and  therefore  the  coudeusation  and  vacuum  would 
be  decreased  in  the  ratio  of  the  decreased  motion  of  the 
propelling  engine. 

It  will  also  be  seen  that,  by  reason  of  the  working  of 
the  pump  which  impels  the  water  for  the  condensation  by 
means  of  an  auxiliary  engine,  and  the  double  connection  of 
the  condenser  with  the  waste-pipe  of  the  boiler  or  boilers, 
and  with  the  exhaust  of  the  propelling-engine,  whenever  the 
safety-valve  is  opened,  the  steam  issuing  therefrom,  instead 
of  being  wasted,  will  be  carried  through  the  condenser  and 
condensed,  to  be  returned  to  the  boiler,  thus  avoiding  the 
necessity  of  a  separate  supply  of  water  to  make  up  for  the 
waste  by  the  escape  of  steam  from  the  safety-valve ;  and 
that  when  the  propelling-engine  is  at  rest  the  condenser 
can  be  used  for  the  distillation  and  production  of  fresh 
water  for  any  desired  purpose  on  board  ship,  for  the  con- 
denser is  thus,  when  desired,  rendered  entirely  independent 
of  the  propelling-engine. 

By  passing  the  current  of  steam  in  a  direction  the  reverse 
of  the  current  of  condensing-water,  the  greatest  amount  of 
caloric  is  extracted  with  the  least  amount  of  water. 

The  condensing-water  in  its  passage  through  the  condenser 
never  reaches  the  point  of  evaporation,  and  therefore  mineral 
and  other  matter  held  in  solution  will  not  be  deposited  to 
encrust  the  apparatus ;  and  by  ensuring  a  constant  and  rapid 
current  of  water  around  the  tubes  the  danger  of  unequal 
contraction  and  expansion  is  reduced  to  the  smallest  amount, 
and  so  small  as  to  prevent  all  injurious  effects  by  the  mode 


424  8UBFACI!  CONDENSATION.  chap.  xxix. 

above  described  of  connecting  one  of  the  diaphragms,  to 
wliich  one  end  of  the  tubes  is  attached,  with  the  cylinder 
by  means  of  the  conical  or  bent  ring  or  flange. 

Although  I  have  described  the  use  of  a  rotary  pump, 
operated  by  a  reciprocating  engine,  for  impelling  the  con- 
densing-water  throi;gh  the  condenser,  I  do  not  wish  to 
confine  myself  to  the  use  of  either  a  rotary  pump  or  a  re- 
ciprocating engine  for  this  piii'pose,  as  a  rotary  engine  may 
be  substituted  for  the  reciprocating,  and  a  reciprocating 
pump  for  the  rotary ;  but  I  have  described  and  represented 
this  arrangement  as  the  one  which  I  have  successfully  es- 
sayed and  deem  the  best. 


CHAPTER  XXX. 

THE  CALORIC  ENGINE. 

A1>PLICATI0N    OF   HEATED    AIR   AS   A    JIOTOK. 
(SEE   PLATES   44   AND   45.) 


Engineers  are  aware  tliat  I  built  a  caloric  engine  in 
London,  1833,  operated  by  heated  atmospheric  air;  Faraday, 
Ure,  and  Lardner  taking  great  interest  in  the  same  in  con- 
sequence of  its  being  based  on  the  principle  of  returning, 
at  each  stroke  of  the  working  piston,  the  heat  not  convei-ted 
into  mechanical  work  during  the  previous  stroke.  After  my 
arrival  in  this  country,  1839,  I  prosecuted  the  plan  and  built 
several  caloric  engines  in  succession,  all  of  which  promised 
ultimate  success.  At  each  step  the  dimensions  were  enlarg- 
ed, until  I  produced  an  experimental  engine,  in  1831,  having 
two  working  cylinders  of  seventy-two  inches  diameter,  two 
feet  stroke,  and  two  compressing  cylinders  of  fifty-eight  inches 
diameter  (see  illustrations  on  Plates  44  and  45).  The  lead- 
ing feature  of  this  large  caloric  engine  was  that  of  cii'culating 


426  THE  CALOBIG  ENGINE.  chap.  xxx. 

the  heated  air,  as  it  passed  oft'  from  the  Avorkiug  cylinder, 
throiio'h  a  series  of  Avire  discs  coutaiiiiuo-  au  aow'eii'ate  of 
13,520,000  meshes  for  each  woi'king  cylindei'.  The  cold  air 
iu  entering  the  engine  was  admitted  through  the  meshes  of 
the  heated  discs,  taking  up  nearly  the  whole  of  the  heat 
previously  imparted  by  the  exhaust  air  iu  its  passage  through 
the  meshes,  on  its  way  to  the  atmosphere. 

DESCRIPTION    OF   THE   ILLtTSTEATIONS   KEFEBEED   TO.* 

Fig.  1  represents  a  ti'ansverse  section,  and  Fig.  2  a  longi- 
tudinal section  of  the  engine. 

a,  aii'-receiver.  h  h,  supply-cylinder,  e',  self-acting  valve 
for  letting  air  into,  and  e"  self-acting  valve  for  letting  air 
out  of,  the  same,  c,  supply-piston ;  g\  piston-rod  of  the  same, 
connected  to  the  working-beam  of  the  engine,  d  d,  work- 
ing-cylinder ;  d'  d',  holes  at  the  junction  of  the  two  cylinders, 
through  which  the  atmospheric  air  passes  in  and  out  freely. 
e  e,  working-piston ;  d"  d",  rods  connecting  the  two  pistons 
together,  e'",  air-tight  vessel,  suspended  below  the  working- 
piston,  filled  with  clay  and  charcoal  to  prevent  transmission 
of  heat  from  below,  f  f,  regenerator ;  f,  discs  of  wire-net, 
placed  vertically  in  the  regenerator-box.  g,  valve,  Avoi'ked 
by  the  engine,  for  admitting  air  into  the  regenerator  and 
working-cylinder ;  h,  valve  for  letting  air  out  of  the  same. 
i  i,  pipe,  open  to  the  atmosphere,  for  carrying  off  the  air  after 
having  passed  through  the  engine ;   h,  fire-place. 

The  operation  of  the  engine  is  briefly  as  follows :  A  slow 

*  Copied  from  Appleion's  Magazine  of  1853. 


cn.vr.  XXX.  THE  CALORIC  ENGINE.  427 

fire  being  kept  up  at  h  for  alxiut  two  lioiiis,  until  the 
various  parts  contained  within  the  hriek-woi'k  isliall  liave 
become  moderately  heated,  the  air-receiver  is  charged  by 
means  of  a  haud-pnmp.  As  soon  as  the  internal  pressure 
shall  have  reached  about  six  pounds  to  the  scpiare  inch — 
invai'iably  effected  in  less  than  two  minutes — tlie  liand-pump 
is  stopped,  and  the  valve  g  opened  by  a  starting  levei-,  as 
in  steam-engines;  the  compressed  air  from  the  receiver,  thus 
admitted  under  the  valve  g,  rushes  through  the  partially 
heated  wires  /'  into  the  working-cylinder,  forcing  its  piston 
e  upwards,  as  also  the  supply-piston  c,  by  means  of  the  con- 
necting-rods d"  d".  The  atmospheric  air  contained  in  the 
upper  part  of  cylinder  h  will,  by  this  upward  movement  of 
the  supply-piston,  l)e  forced  througli  the  valve  e"  into  the 
air- receiver.  When  the  working-piston  has  reached  three- 
fourths  of  the  full  stroke,  the  valve  g  is  closed  by  the  engine ; 
and  when  the  piston  has  arrived  at  the  full  np-stroke,  the 
valve  li  is  opened.  A  free  coininniiication  with  the  atmo- 
sphere being  thereby  established  by  means  of  the  open  pipe 
i  i,  the  air  under  the  w^orking-piston  passes  off,  and,  owung 
to  the  removal  of  pressure  under  the  working-piston,  it  will 
instantly  begin  to  descend  by  its  ow'u  ^veight. 

The  heated  air  from  under  the  working-piston,  in  pass- 
ing off  through  the  ^vires  f,  gives  out  its  caloric  to  the 
same  so  effectually  that,  on  reaching  the  thermometer  in,  the 
temperature  never  e.vceeds  that  of  the  entering  air  at  7  b}' ' 
more  than  30°;  on  the  other  hand,  the  cold  air  from  the 
receiver,   in    circulating   through   the  meshes   of   w^ires  in   its 


428  TEE  GALOBIC  ENGINE.  chap.  xxx. 

passage  to  tlie  working  cylinder,  becomes  so  effectually 
heated  that,  on  passing  n,  its  temperature  is  invariably 
increased  to  upwards  of  450°  wlien  tlie  machine  is  in  full 
operation. 

It  is  evident  that  during  the  descent  of  the  supply-piston 
G  the  outlet  valve  e"  remains  closed  by  the  pressure  from  the 
receiver,  whilst  the  inlet  valve  e'  is  kept  open  by  suction, 
and  hence  that  a  fresh  quantity  of  atmospheric  air  enters 
the  supply-cylinder  at  each  down-stroke  of  its  piston,  and 
by  the  up-stroke  is  forced  into  the  receiver.  There  being 
two  supply-cylinders  of  alternating  action,  a  constant  supply 
of  fresh  air  into  the  receiver  is  obtained  for  feeding  the 
working-cylinders. 

It  need  hardly  be  stated  that  the  smaller  quantity  ob- 
tained by  the  supply-cylinder  suffices  to  fill  the  larger 
capacity  of  the  working-cylinder,  in  consequence  of  the  in- 
crease of  volume  attending  the  increase  of  temperature  ;  nor 
need  it  be  stated  that  an  equal  amount  of  force  is  exerted 
by  the  up-and-down  movement,  as  there  are  two  pairs  of 
cylinders  attached  at  opposite  ends  of  a  common  working- 
beam. 

The  foregoing  description  being  deemed  sufficient  to  ex- 
plain the  mechanical  operation  of  the  engine,  the  result  of 
its  prolonged  trial  may  now  be  considered  ;  but,  before  doing 
so,  it  will  be  well  to  state  some  particulars  in  relation  to 
the  regenerator.  The  regenerator  measures  26  inches  in  height 
and  width  internally ;  each  disc  of  Avire  contains  G76  superfi- 
cial  inches,   and   the   net  has    10    meshes  to  the  inch ;    each 


CHAP.  XXX.  THE  CALOEIG  EXGINE.  429 

superficial  inch,  therefore,  contains  100  meshes,  which,  multi- 
plied by  676,  gives  67,600  meshes  in  each  disc;  200  discs 
being  employed,  it  follows  that  each  regenerator  contains 
13,520,000  meshes,  and,  consequently,  if  we  consider  that 
there  are  as  many  small  spaces  hehceen  the  discs  as  there 
are  meshes,  we  shall  find  that  the  air  within  the  regene- 
rator is  distributed  in  27,000,000  minute  cells.  Theory 
clearly  indicates  that,  owing  to  the  small  capacity  for  heat 
of  atmospheric  air  (that  beneficial  property  which  the  Great 
Mechanician  gives  to  it  as  a  fit  medium  for  animated  loann 
beings  to  live  in),  and  in  consequence,  also,  of  the  almost  infi- 
nite subdivision  among  the  wires,  the  temperature  of  the 
circulating  air,  in  passing  through  the  regenerator  of  the 
caloric  engine,  must  be  greatly  changed.  Practice  has  fully 
realized  all  that  theory  predicted,  for  the  temperatures  at  x 
and  z  have  never  varied  during  the  trials  less  than  350°, 
when  the  engine  has  been  in  full  operation  ;  indeed,  it  has 
been  found  impossible  to  obtain  a  differential  tenijjerature  of 
less  magnitude,  with  sufficient  fii'es  in  the  furnaces. 

The  reason  is  evident :  the  cold  air  from  the  receiver  is 
half  the  time  playing  upon  the  wire  discs  at  x,  whilst  the 
heated  air  from  the  working-cylinder  is  playing  during  the 
other  half  on  the  wire  discs  at  z ;  as  no  heated  air  can 
reach  the  former  without  passing  througb  the  regenerator, 
and  as  no  cold  air  can  reach  the  discs  at  z  before  likewise 
passing  all  the  ^dres,  it  follows  that  the  establishing  an  equi- 
librium of  temperature  becomes  impossible.  The  great  num- 
ber of  discs,  their  isolated  character,  anil    the    before-named 


430  THE  CALORIC  ENGINE.  chap.  xxx. 

distribution  of  tlie  air  in  sucli  a  vast  number  of  minute  cells, 
readily  explain  the  surprising  fall  and  increase  of  tempera- 
ture of  tbe  opposite  currents  passing  the  regeneratoi',  and 
'which  constitutes  the  grand  feature  of  the  caloric  engine, 
effecting,  as  it  does,  such  an  extraordinary  saving  of  fuel  by 
rendering  the  caloric  not  converted  into  mechanical  Avork 
active  over  and  over  again. 

In  further  explanation  of  the  wonderful  efficiency  of  the 
regenerator,  it  may  be  stated  that  each  disc  contains  1,140 
feet  of  wire  in  length,  and  each  regenerator  228,000  feet, 
or  41^  miles,  of  Avire;  the  superficial  measurement  of  which 
is  2,014  square  feet,  Avhich  is  equal  to  the  entire  surface  of 
four  steam-boilers  forty  feet  long  and  four  feet  diameter; 
and  yet  the  regenerator  displaying  that  amount  of  heating 
surface  is  only  two  feet  cube,  less  than  rsVir  of  the  bulk  of 
said  boilers  ! 

In  ]'egard  to  loss  of  Jieat,  the  result  of  ample  trial  has 
been  that  at  no  time  has  the  temperature  of  the  escaping 
air  at  m  exceeded  that  of  the  entering  air  at  I  by  more  than 
30°.  As  this  differential  temperature  exhibits  the  positive 
loss  of  Iieat,  it  becomes  important  to  ascertain  its  amount  in 
pounds  of  coal :  the  area  of  the  supply-piston  is  2,626  square 
inches,  and  its  stroke  two  feet ;  hence  36to  cubic  feet  of 
atmospheric  air  is  supplied  for  each  stroke,  and  therefore 
at  30  strokes  1,092  cubic  feet,  and  for  both  cylinders  2,184 
cubic  feet  per  minute  =  131,040  cubic  feet  per  hour.  The 
Aveight  of  atmospheric  air  is  nearly  13i  cubic  feet  to  the 
pound,   and   hence   it  Avill  be  seen  that   9,706  pounds  of  air 


CUAI'.  XXX.  TUE  CALOUIC  EiiGlKE.  431 

pass  tlirougli  the  engine  every  liuiir.  We  kuo\v  tliat  one 
pound  of  coal  will  raise  tlie  temperature  of  10  pounds  of 
water  1,100',  while  the  specific  heat  of  water  is  to  that  of 
the  air  as  I'li  :  100;  hence  it  will  be  seen  that  38iV  pounds 
of  air  will  be  elevated  in  temperature  1,100°  with  one  pound 
of  coal.  Now,  the  observed  loss  of  heat  in  the  engine  being 
30°,  the  fact  will  be  established  that  the  loss  will  amount 
to  one  pound  of  coal  for  every  1,408  pounds  of  air  passed 
through  the  engine,  \vhich,  on  9,706  pounds,  proves  the 
actual  loss  of  heat  in  both  regeneratoi-s  to  be  only  6^u  pounds 
of  coal  2)er  hour.  A  pressure  of  13  pounds  being  sustmned 
in  the  receiver,  exerting  GO  horse-power  with  an  actual  waste 
of  only  G.8  pounds  per  hour,  it  \vill  be  found  that  Iwo 
ounces  of  coal  per  hour  per  horse-power  is  the  quantity  of 
fuel  absolutely  wasted  in  the  process  of  transfer.  The  actual 
consumption  of  the  engine  is,  however,  nearly  4:0  pounds 
per  hour,  which  is  thus  proved  by  the  foregoing  to  be  chieily 
carried  off  by  radiation  of  heat.  On  a  large  scale  much  of 
that  radiation  \v\\\  be  prevented.  As  the  machine  stands,  an 
indicated  horse-power  is  produced  by  a  consumption  of  less 
than  11  ounces  to  the  horse-power  per  hour. 

The  following  particulars  are  of  considerable  practical 
importance : 

Ist.  The  valves  g  and  h  are  not  subjected  to  heat,  the  calo- 
ric being  taken  up  by  the  wires  before  reaching  the  valves. 

2d.  The  temperature  of  the  packing  of  the  working-pistons 
does  not  exceed  boiling  heat  at  any  time,  proving  the  efficacy 
of  the  heat-intercepter  e'". 


432  TEH  CALOEIC  ENGINE.  chap.  xxx. 

3d.  As  only  a  slow  radiating  fire  is  needed,  it  has  been 
found  that  common  whitewash,  applied  to  the  under  side  of 
the  heater,  remains  for  several  weeks,  proving  conclusively 
that  the  effect  of  the  heat  is  quite  harmless. 

4th.  A  hole  of  half  an  inch  diameter,  kept  open  for 
several  hours,  in  the  valve-chest,  under  the  inlet-valve  g, 
does  not  sensibly  aflfect  the  pressure  in  the  receiver  a,  so 
abundant  is  the  supply  of  air.  This  fact  has  surprised  all 
practical  men  who  have  witnessed  the  operation  of  the  en- 
gine. It  proves  completely  that  the  machine  need  not  be 
perfectly  air-tight,  as  supposed  by  many. 

5th.  After  putting  a  moderate  quantity  of  fuel  into  the 
furnace,  it  has  been  found  that  the  engine  works  with  full 
power  for  three  hours  without  fresh  feed,  and,  after  remov- 
ing the  fires  entirely,  it  has  frequently  worked  for  one  hour. 

The  regularity  of  action  and  perfect  working  of  every 
part  of  this  experimental  engine,  and,  above  all,  its  apparent 
great  economy  of  fuel,  induced  some  enterprising  merchants 
of  New  York,  in  the  latter  part  of  1851,  to  accept  my  pro- 
position to  construct  a  ship  for  navigating  the  ocean  propelled 
by  paddle-wheels  actuated  by  the  caloric  engine.  This  work 
was  commenced  forthwith,  and  pushed  with  such  vigor  that 
within  nine  months  from  commencing  the  construction  of  the 
machinery,  and  within  seven  months  from  laying  the  keel, 
the  j)addle-wheels  of  the  caloric  ship  Ericsson  tui'ued  round 
at  the  dock  !  In  view  of  the  fact  that  the  engines  consisted 
of  four  working-cylinders  of  168  inches  diameter,  6  feet 
stroke,  and  foiir  air-compressing  cylinders  of  137  inches  dia- 


CHAP.   XXX. 


THE  CALORIC  ENGINE. 


433 


meter,  6  feet  stroke,  it  may  be  claimed  that,  in  point  of  mag- 
nitude and  rapidity  of  construction,  the  motive  machinery  of 
the  caloric  ship  stands  uin-Ivalled  in  the  annals  of  marine 
engineering.  It  may  be  added  that  the  principal  eugineei's 
of  New  York  all  expressed  the  opinion  that  a  better  speci- 
men of  ^vorkIllalls^lip  than  that  presented  by  the  huge 
engines  of  the  caloric  ship  had  not  been  produced  by  our 
artisans  up  to  that  time. 

The    following  data,  published  in  Appletons'   Meclicmic^ 
Magazine,  will  interest  the  professional  reader: 


DnCENSIONS    OF    THE    ERICSSOM', 


Length  on  deck, 

260  feet 

Length  of  keel,        ..... 

250     " 

Breadth  of  beam, 

40     " 

Depth  of  hold,         .... 

27     " 

Draught  of  water  on  trial-trip. 

17     " 

Diameter  of  wheels,          ..... 

32     " 

Length  of  bucket, 

lOi  " 

Breadth  of  bucket,           .... 

20  ins. 

Dip  of  wheel  (supposed  about), 

2  feet 

ENGINES. 

Number  of  working-cylinders  or  single-acting 

air-engines,  ......  4 

Diameter,  .  168  inches. 

Area  of  piston,          .....         22167.07  sq.  in. 
Stroke, 6  feet. 


434 


THE  GALOEIO  ENGINE. 


CHAP.    XXX. 


Portion    of     stroke    from     commencement    at 

which  air  is  "  cut  off "  (about),  .         .  t^ 

Cubical  contents  of  each  working-cylinder,        1596024  cub.  in. 
Cubical  contents  of  t^  of  working-cylinder,      995495       " 
Number    of    suppl3'-c}linders    or    single-acting 

pumps, 4 

Diameter,  ...... 

Area  of  jjiston  or  plunger, 

Stroke,  necessarily,    ..... 

Cubical  contents  of  each  pump. 

Number  of  regenerators, 

Number  of  discs  of  iron-wire  netting  in  each 

regenerator, 

Height  of  each  disc,         .... 

Width, 

Size  of  wire,      ...... 

Eatio  of  area  of  openings   in   the   netting  to 

total  area  of  disc,        ..... 
Total  area  of   opening   of    "  air- way  "  through 

n     n-        6X4 
each  disc,  = 12  sq.  ft. 

Greatest  or  total  heat  .of  air  in  working- 
cylinder  above  atmosphere,          .         .         .  384°  F. 

Heat  of  issuing  air  above  atmosphere,     .         .  30°  F. 

Pressure  necessary  to  move  the  engine,            .  i  lb. 

Coal  consumed  in  the  four  furnaces  per  day,  6  tons. 

Maximum    coal    possible    to    consume    in   the 

four  furnaces  per  day,         ....  7    " 


137 

inches 

.     14741 

sq.  in. 

•6  feet. 

1061352 

cub.  in 

4 

1 

50 

6 

feet. 

4 

a 

tV 

incli. 

i  to  1 


CUA1>.   XXX. 


TUi:   CALORIC  EyuLSE. 


435 


Number  of  smoke-pipes,  .....  2 

Number  uf  alr-pipet<,         .....  2 

Height  oi  each  smoki-  ami  air  pipe  above  deck,  1-*  feet. 

Diameter       "  "  "  "  30  inches. 

Amount  of  air  passing  through  the  four  cylin- 
ders per  houi',     ......     50  to  75  tons. 

Depth  of  ^vorking•piston,  or  thickness,    .         .  6  feet. 

Thickness  of  cylinder-bottom,  .         .         .  1^  inches. 

Distance  of  grate  from  bottom  of  cjdinder,    .  5  feet. 

Ordinary  pressure  of  the  engine  per  sq.  incli,  12  lbs. 

Actual  pressure  on  the  second  trial-trip,  Jan- 
uary 11, •       .         .  8    " 

Number    of    revolutions    under    pressure    of 

8  lbs.  on  trial  trip,     .....  9 

Number  of  revolutions  expected  with   12  lbs. 

pressure,       .         .         .         .         .         .         .  12 

Miles  per  hour  obtained  on  trial-trip,  Jan- 
uary 11,  allowing  for  tide,  etc.,  .         .  7 

Miles  per  hour  expected  with  12  lbs.  pressure,  10  to  12 

Number  of  meshes  in  each  disc,     .         .         .  500000 

Temperature  in  working-cylinder,  60°  +  384°  =  444° 

Common  temperature  of  the  atmosphere  (usual 

assumption), 60° 

Specific  heat  of  air — water  being  1000,  .         .  .2669 

Common   pressure    of   air   per  square   inch  ~ 

14.73  lbs.,  say 15  lbs. 

Weight  per  cubic  foot,  common   pressure  and 

temperature  =  .0752914  ll>.s.,  say  .         .  1*3  lb. 


436  THE  OALOBIO  ENGINE.  chap.  xxx. 

Density  of  air,  temperature  remaining  con- 
stant, is  directly  as  tlie  pressure. 

Weight   per   cubic  foot,  at    12   lbs.   pressure, 

common  temperature,  ....  t¥j 

Expansion  of  air  at  32°  for  each  degree  add- 
ed, according  to  Rudberg,  .         .         .  ri? 

Dalton  and  Gay-Lussac,  .00208  ;  Regnault,  rh ; 

common  estimate,         ....  rh 

Expansion  of  air  at  60°,  for  the  384°  added,  |f| 

Density  of  air  at  (60°  +  384°  =)  444°,   com- 

n       .  n       •  o  508 

pared  with  air  at  60  ,  as    .         .         .  „„    , to  1 

^  508  +  384 

Weight  of    a  cubic  foot   at   12  lbs.   pressure, 

temperature  444°  =  M  X  AV  =  .         .         tVWA  lb. 

Weight  of  995495  cubic  inches  at  12  lbs.  pres- 
sure, temperature  444°  =  HffF  X  tWs^o  =  46  lbs. 

Therefore,  air   passed    through    each    cylinder 

each  stroke,  .         .         .         .         .         ,  46  " 

Weight  of  1061352   cubic  inches,  at   common 

temperature  and  pressure  =  ^  Wh^i  ^  X  ^  —       47.153  lbs. 

Therefore,  air  passed  each  pump  each  stroke,  47  " 

Allowance   made   for   clearance,  leakage,    etc., 

per  stroke,  47  —  46  =  .         .         .         .  1  lb. 

Units  of  heat  required  to  raise  47  lbs.  air  384° 
=  47  X  384  X  .2669  =         .         .         .         . 

Units  of  heat  retained  by  the  47  lbs.  on  es- 
caping =  47  X  30  X  .2669  =       .         .         . 

Units  of  heat  transferred  each  stroke,    , 


4817 

units. 

376 

11 

4441 

li 

CIIAP.   XXX. 


THE  CALORIC  ENGINE. 


437 


Absolute  theoretical  consumption  of  heat  per 
stroke,  per  cylinder,     ..... 

Mean  pressure,  per  square  inch,  on  ^vorkiug■ 
piston,  allowing  for  continued  addition  of 
heat  while  expanding,  initial  pressure  being 
13  lbs.,  about 

Mean  force  acting  upon  working-piston,  10.8  X 
22167  =        

Mean  resistance  per  square  inch  to  supply  pis- 
ton, commencing  with  0  and  increasing  to 
12  lbs.,  at  which  pressure  it  continues  to 
end  of  stroke. 

[The  mean  resistance  in  compressing  an  elas- 
tic fluid  may  be  found  by  reversing  the 
ordinary  calculation  on  expansive  working. 

The  hyp.  log.  of  M  is  .588]  1.588  X  12  X  H  = 

Mean  resistance  against  supply-piston  10.55  X 
14741  =       

Balance  tending  to  move  the  engine,  239403 
-  155598  =         

Units  of  power  theoretically  obtainable  per 
stroke  =  83805  X  G  = 

Units  of  power  theoretically  obtainable  from 
each  unit  of  heat, 


37G  units. 


10.8  lbs. 


239403.6    " 


10.55  lbs. 


155598  " 


83805  " 


502830  units. 


1337 


The  ship  after  completion  made  a  successful  trip  from 
New  York  to  Washington  and  back  during  the  winter  season  ; 
but    the   average   speed  at  sea   proving  insufficient  for  com- 


438  THE  CALOIUC  EXGINE.  chap.  xxx. 

mercial  purposes,  the  owners,  v^'ith  regret,  acceded  to  my 
proposition  to  remove  the  costly  machinery,  although  it  had 
proved  perfect  as  a  mechanical  combination.  The  resources 
of  modern  engineering  having  been  exhausted  in  producing 
the  motors  of  the  caloric  shij?,  the  important  question  has 
for  ever  been  set  at  rest :  Can  heated  air  as  a  mechanical 
motor  compete  on  a  large  scale  with  steam  ?  The  commercial 
world  is  indebted  to  American  enterprise — to  New  York 
enterprise — for  having  settled  a  question  of  such  vital  im- 
portance. The  marine  engineer  has  thus  been  encouraged 
to  renew  his  efforts  to  perfect  the  steam-engine,  without 
fear  of  rivalry  from  a  motor  depending  on  the  dilatation  of 
atmospheric  air  by  heat. 

The  engines  of  the  caloric  ship  being  an  exact  counter- 
j)art  of  the  experimental  engine  of  1851,  excepting  dimensions, 
a  description  has  been  deemed  superfluous.  It  may  be  men- 
tioned, however,  that  the  pair  of  engines  in  the  caloric  ship 
actuated  a  single  crank  in  the  middle  of  the  paddle-shaft 
by  connecting-rods  working  at  right  angles  on  a  common 
crank-pin,  as  in  all  my  marine  engines. 


CHAPTER   XXXI. 

CALOKIC    ENGINE    FOR   DOMESTIC    PUEPOSES. 

(SEE   PLATE   46.) 


Although  the  caloric  engine  has  proved  inapplicable  to 
navigation,  it  has  been  found  to  be  of  very  great  utility  as 
a  domestic  motor,  and  for  all  pui-poses  demanding  a  small 
amount  of  motive  power. 

The  following  interesting  article  from  the  New  York  Tri- 
hune  of  May  5,  1860,  shows  how  rapidly  the  caloric  engine 
was  adopted  after  its  adaptation  to  domestic  purposes : 


■  THE   NEW    MOTOR. 


"It  is  some  eighty-six  yeai-s  since  ^Ir.  Boulton,  at  the 
great  steam-engine  works  of  Soho,  made  use  of  the  memorable 
expression  to  Eoswell :  '  I  sell  here,  sir,  what  all  the  world 
desires  to  have — Poweu.'  The  mechanical  world  has  been 
occupied  from  that  time  to  the  present  \vith  this  problem 
of  power,  and  mechanical  ingenuity  has  tasked  and  exhausted 


440  TEE  DOMESTIC  CALORIC  ENGINE.  CHAP.  XXXI. 

itself  witli  efforts  to  construct  a  macliine  that  sliould  prove 
an  efficient  auxiliary  or  rival  of  the  steam-engine.  And  it 
is  most  extraordinary  that,  notwithstanding  the  amount  of 
inventive  genius  and  science  that  has  been  expended  in  this 
special  field  of  labor,  literally  nothing  had  been  accomplished 
of  any  practical  importance  till  Ericsson  produced  the  caloric 
engine,  in  the  particular  form  and  with  the  peculiar  devices 
which  distinguish  it  from  all  the  engines  actuated  by  heat, 
that  have  been  built  at  such  an  enormous  expense  of  time 
and  money. 

"  Motive  engines  of  a  moderate  or  even  of  a  small  power 
play  a  very  important  part  in  the  economy  of  human  life. 
The  frightful  horrors  of  the  slave-trade ;  the  scarcely  less 
frightful  hoi'rors  of  the  traffic  in  Coolies;  nay,  the  haggard 
features  and  jaded  limbs  that,  in  our  great  cities  more  espe- 
cially, speak  so  distinctly  of  over-wrought  human  labor,  and 
cry  out  so  emphatically  for  relief — all  these  demonstrate  that 
a  compact,  manageable,  safe,  and  economical  motor,  adequate 
to  the  work  of  a  single  slave  or  Cooly,  or  overtasked  white 
man  or  white  woman,  would  do  more  to  mitigate  the  suffer 
ing  and  diminish  the  drudgery  of  mankind  than  any  other 
conceivable  invention.  After  all  the  enormous  accumula 
tions  of  steam-power,  water-power,  wind-power,  and  horse 
power,  and  their  vast  achievements,  by  how  much  the  larger 
amount  of  power  exercised  in  the  world  is  the  aggregate 
result  of  individual  force  applied  to  the  thousands  of  little 
things  that  occupy  the  human  family  in  the  daily  routine  of 
living!     Combine  these  forces,  and  what  a  stupendous  whole 


CHAP.  XXXI.  THE  DOMESTIC  CALORIC  EXdlNE.  441 

tliey  exhibit !  Make  au  availal)le  motor  that  shall  be  of 
oue-inan  power,  and  what  a  result  is  obtained !  Make  a 
motor  pei-fectly  safe,  easily  kept  in  order,  requiring  no  water, 
and  consuming  but  little  fuel,  of  the  power  of  a  single  horse, 
to  what  an  extent  the  aggregate  result  is  augmented,  and 
what  an  importance  in  human  affairs  such  a  machine  assumes  ! 

"  If  Ericsson's  caloric  engine,  then,  claimed  to  be  nothing 
but  such  a  motor,  it  would  be  a  subject  well  deserving  the 
most  earnest  and  serious  investigation ;  but  the  proof  is  accu- 
mulated, of  a  nature  that  compels  belief  and  defies  contra- 
diction, which  demonstrates  the  existence  in  this  engine  of 
a  power  entirely  sufficient  for  all  but  a  very  few  of  the 
thousand  uses  for  which  power  is  requii'ed. 

"  It  is  not  material  to  our  pur2:)ose  to  indulge  in  any 
retrospective  review  of  Ericsson's  labors.  It  is  well  known 
that  this  grand  invention  has  occui:)ied  thirty  years  of  his 
life,  during  which  he  has  built  many  engines  of  the  largest 
size  and  uncounted  experimental  engines  of  smaller  power. 

"We  have  seen  an  official  statement  in  relation  to  an 
engine  put  up  about  a  year  since  to  supply  the  locomotives  at 
the  South  Groton  Station,  on  the  Fitchburg  Railroad.  From 
April,  1859,  to  April,  1860,  this  engine  pumped  1,600,000  gal- 
lons of  water,  at  an  expense  to  the  company  for  fuel  and  oil 
of  $25,  and  for  an  '  engineer '  $25,  and  has  not  cost  one  cent 
for  alteration  or  repairs. 

"A  result  more  irapoitant,  in  view  of  the  number  of 
engines  employed,  is  exhibited  on  the  New  York  Central 
Railroad,  on  the  line  of  which  there  are  now  some  twenty 


442  THE  DOMESTIC  CALORIG  ENOTNE.  chap.  xxxi. 

of  ttese  engines  in  daily  use.  Mr.  Chaimcey  Vibbard,  the 
Superintendent  of  that  road,  reports,  over  his  official  signa- 
ture, after  several  months'  experience  with  a  number  of  these 
engines,  that  they  peiform  an  '  incredible '  amount  of  labor 
'for  the  small  quantity  of  fuel  consumed.'  One  of  them,  he 
says,  for  t\V  of  a  cent  per  hour,  does  the  woi'lv  formerly 
done  by  foxir  men  at  an  expense  of  $25  each  per  month. 
Another,  of  the  same  size,  at  the  Savannah  Station,  at  an  ex- 
pense of  eleven  cents  a  day,  does  the  work  of  five  men  ^vho 
received  $125  a  month.  Other  engines  have  been  erected 
on  several  other  I'ailroads  for  pumping  purposes  with  the 
same  favorable  result. 

"The  second  application  of  the  caloric  engine  was  to 
the  driving  of  printing-presses.  The  first  trial  of  the  engine 
for  this  purpose  was  made  in  the  office  of  the  Hartford 
Itnies ;  the  first  that  was  entirely  successful  was  made  in 
the  office  of  T.  W.  Strong,  No.  98  Nassau  Street,  in  this 
city.  The  next  engine  built  was  set  up  in  the  office  of 
Messrs.  French  &  Wheat,  No.  18  Ann  Street,  and  the  third 
in  the  office  of  Mr.  C.  C.  Shelley,  a  job-printer  in  Barclay 
Street.  The  result  has  been  the  adoption  of  the  engine  in 
numerous  job-offices  in  every  part  of  the  country.  There  are 
now  no  less  tlian  forty  daily  papers  in  the  United  States 
printed  by  Ericsson's  engines,  most  of  them  of  24-inch,  but 
three  or  four  of  12  and  18  inch  cylinders.  One  of  the  most 
recent  testimonials  to  its  value  is  fi-om  the  proprietor  of  the 
Savannah  Evening  Express,  who  states  that  lie  regards  it  as 
the  most  perfect  and  economical  motive  power  ever  applied." 


CUAP.  XXXI.  TIIK  DOMESTIC  CALORIC  EXGIXE.  443 

Several  tLousand  caloric  engines  were  subsequently  con- 
structed in  this  country  and  in  Europe ;  but  steam-engineers, 
finding  by  the  extraordinary  demand  for  caloric  engines  that 
very  moderate  power  A\as  a  great  desideratum,  have  pei-fected 
the  steam-motor  until  it  almost  rivals  the  caloric  engine  iu 
sjxfety  and  adaptability  ;  consequently,  the  demand  for  caloric 
engines  has  been  greatly  diminished  of  late.  Yet  this  motor 
can  never  be  superseded  by  the  steam-engine,  since  it  requires 
no  water,  besides  being  absolutely  safe  fi'om  explosion.  There 
are  innumerable  localities  in  which  an  adequate  quantity  of 
water  cannot  be  obtained,  but  \vliere  the  necessities  of  civi- 
lized life  call  for  mechanical  motors  ;  hence  the  caloric  engine 
may  be  regarded  as  an  institution  inseparable  from  civiliza- 
tion. It  should  be  stated  that  the  caloric  engine  has  been 
found  to  furnish  the  only  rt'liable  motive  power  for  operating 
the  fog-signals  on  our  coasts.  The  following  statement,  pre- 
sented to  the  Light-House  Board,  sets  forth  very  clearly  the 
advantages  of  the  air  motor  for  the  purpose  mentioned : 

With  reference  to  the  important  question  whether  steam 
is  a  proper  motive  power  for  actuating  the  mechanism  con- 
nected with  fog-signals,  I  beg  to  express  the  opinion  that 
unless  a  safer  motor  can  be  found  than  the  steam-engine — 
more  particularly  a  high-pressure  steam-engine — the  great 
practical  benefit  which  you  expect  from  the  contemplated 
system  of  fog-signals  will  never  be  realized.  My  reason  for 
expressing  this  opinion  will  be  found  in  the  following  brief 
summary:  1.  A  high-pressure  steam-boiler,  even  when  sup- 
plied w  ith  pure,  fresh  water,  is  an  apparatus  which  demands 


444  THE  DOMESTIC  CALOIilC  ENGINE.  CHAP,  xxxi, 

the  constant  attention  of  an  experienced  person.  Considering 
that  any  neglect  in  keeping  up  the  feed  in  the  boiler  will 
inevitably  result  in  an  explosion,  it  is  highly  imprudent  and 
scarcelj-  humane  to  put  such  an  instrument  in  the  hands  of 
a  light-house  keeper.  Let  us  reflect  on  the  well-known  fact 
that  when  a  boiler  foams  even  the  practised  engineer  is 
sometimes  at  a  loss  to  determine  the  height  of  water  within. 
2.  Apart  from  the  difficulty  and  danger  thus  alluded  to, 
another  circumstance  presents  itself  connected  with  the  em- 
ployment of  steam,  which  is  practically  insuperable,  viz., 
that  brackish  or  salt  ^vater  must  be  resorted  to  in  most 
localities.  Accordingly,  unless  a  certain  quantity  of  the  salt 
water  is  regularly  drawn  off  and  replaced  by  water  less 
impregnated  with  saline  matter,  the  boiler  will,  at  best,  be 
rendered  useless  by  the  dej)osit  formed.  In  most  cases  the 
first  warning  to  the  unskilful  light-house  keeper  will  pro- 
bably be  the  explosion  of  the  boiler. 

In  connection  with  this  most  important  matter,  I  cannot 
omit  adverting  to  the  fact  that  the  employment  of  salt 
water  for  land  engines  attended  by  skilful  engineers  has 
been  found  so  impracticable  that  means  of  procuring  fresh 
water — in  many  cases  at  very  great  cost — have  been  deemed 
indispensable.  It  is  only  in  the  steam-ship,  where  the  most 
competent  engineers  are  employed,  provided  with  salinometers 
and  other  instruments,  that  it  has  been  found  practicable  to 
employ  salt  water.  But  even  in  the  steam-ship  salt  feed  has 
been  dispensed  with  by  employing  the  surface-coudeuser  as 
the  only  certain  means  of  saving  the  boilers  from  incrustation. 


CHAP.  XXXI.  THE  DOMESTIC  CALOEIC  £yGIXE.  445 

3.  During  cold  weather,  another  serious  difficulty  will 
be  encountered  if  you  employ  steam,  which  calls  for  the 
application  of  costly  and  complicated  conti'ivances.  Unless 
the  boiler  is  constantly  under  steam,  it  must  be  kept  in  some 
place  adequately  heated  by  stoves  to  prevent  pumps,  pipes, 
and  cocks  from  freezing.  Not  oiil}-  this,  the  cistern  Itself, 
which  is  to  supply  the  boiler,  will,  on  our  iuclenient  coast, 
freeze  unless  warmed  by  some  means.  I  need  scarcely  remind 
you  that,  in  many  localities,  the  entire  supply  of  water  will 
^vholly  fail  during  continued  cold,  dry  weather.  In  fine, 
the  disadvantages  of  steam  for  any  general  system  of  fog- 
signals  are  so  numerous  and  formidable  as  to  render  the  very 
proposition  to  employ  that  agent  an  absurdity. 

Having  thus  briefly  disposed  of  the  question  of  employ- 
ing steam  as  the  motive  power  for  actuating  the  machinery 
of  your  pi'oposed  fog-signals,  I  have  now  to  state  that  long 
practice  has  shown  that  the  expansive  force  of  heated  atmo- 
spheric air  furnishes  a  reliable  dr//  motor  wholly  independent 
of  atmospheric  temperature.  The  advantages  of  such  a  raotoi-, 
more  especially  as  it  requires  no  particular  kind  of  fuel, 
are  so  obvious  that  I  will  not  detain  you  by  enumerating 
the  same.  Suffice  it  to  say  that  it  enables  you  to  locate 
your  fog-signal  on  the  dry,  barren  rock  as  well  as  on  the 
moist,  sandy  beach ;  and  that  its  efficiency  is  not  affected 
by  the  most  intense  cold,  and  that,  so  far  from  demanding 
a  heating  apparatus  during  the  inclement  season,  the  light- 
house keeper  will  find  it  a  very  desirable  accessory  in 
warming  his  quarters.     Above  all,  while  it   thus  adds  to  his 


446  THE  DOMESTIC  CALOBIC  ENGINE.  CHAP.  xxxi. 

comfort,  it  carries  no  danger  with  it.  The  worst  that  can 
ha2:)pen  is  that  the  machine  Avill  stop  for  Avant  of  fuel,  or 
that  its  speed  will  slacken  for  want  of  oil  being  applied 
to  the  bearings.  The  caloric  engine  is  now  so  well  known 
that  I  need  not  enter  on  a  description  of  its  construction. 
It  will  be  necessary,  however,  to  advert  to  the  fact  that  the 
caloric  engine  is  more  bulky  and  of  greater  weight  than  the 
steam-engine,  and  that  its  cost  is  some  50  per  cent,  greater. 
These  disadvantages,  however,  as  regards  the  application  to 
fog-signals,  become  trifling,  in  view  of  the  before-named  ad- 
vantages. Indeed,  in  many  places  the  cost  of  procuring  a 
suital)le  supplj^  of  water  will  be  far  greater  than  the  differ- 
ence of  price  of  engine — leaving  out  of  sight  the  impossi- 
bility of  procuring  suitable  water  in   many  cases. 

The  leading  features  of  the  domestic  caloric  engine  will 
be  seen  by  reference  to  Plate  46,  i-epresenting  a  longitudinal 
section  through  the  central  vertical  plane.  Professor  Bar- 
nard having  very  thoroughly  examined  one  of  these  engines 
at  the  Paris  Exhibition,  1867,  I  propose  to  present  a  copy 
of  his  re})ort : 

"  In  its  present  form  the  Ericsson  engine  fails  to  present 
to  the  observer  a  combination  at  first  view  easilj^  intelligible. 
It  even  seems  to  be  characterized  by  a  certain  amount  of 
complication,  which  might  suggest  greater  liability  to  derange- 
ment than  ought  to  belong  to  a  prime  mover.  A  closer 
examination,  nevertheless,  will  show  that  the  mechanism 
itself  is  in  fact  very  simple,  and  that  it  is  only  the  rather 
puzzling  consecution  of  movements  which  confuses. 


CUAP.  XXXI.  THE  DOMESTIC  CALOlilC  EXGINE.  447 

"Before  referring  to  the  figure  of  this  engine,  which  is 
given  in  the  illustnition  on  the  phite  mentioned,  tlie  following 
general  explanation  of  the  mechanical  principles  of  its  con- 
struction will  be  understood.  Let  it  be  supposed  that  a 
piston  moves  air-tight  in  a  cylinder  which  is  closed  at  both 
ends.  Call  one  end  of  the  cylinder  A,  and  the  other  B. 
Call  the  piston  also  C.  In  the  end  A  let  there  be  a  valve 
opening  inward,  and  in  the  end  B  a  second  valve  opening 
outward.  These  two  valves  open,  then,  in  absolute  direction, 
the  same  \vay.  Let  the  piston  C,  furthermore,  have  a  valve 
opening  in  this  common  direction.  Then,  if  the  piston  C 
move  toward  B,  its  own  valve  will  naturally  close,  and  that 
of  B  will  open,  because  the  movement  tends  to  compress 
the  air  between  B  and  C.  Also  the  valve  A  will  open  at 
the  same  time,  because  the  movement  tends  to  rarefy  the 
air  between  A  and  B.  Thus,  in  this  movement,  continued 
to  the  end  of  the  cylinder,  all  the  air  on  the  side  toward  B 
may  be  expelled;  but  at  the  same  time  the  cylinder  ■will 
be  filled  on  the  other  side  toward  A,  l)y  the  influx  of  air 
from  without.  If  the  piston  C  now  revei-se  its  motion,  both 
the  valves  A  and  B  will  be  closed,  because  the  movement 
will  tend  to  rarefy  the  air  on  the  side  of  B,  and  to  con- 
dense it  on  the  side  of  A.  But  its  own  valve  will  be 
opened  by  the  joint  effect  of  these  causes,  so  that  the  air 
will  pass  freely  thiough  the  piston,  and,  if  the  motion  con- 
tinues, will  ultimately  be  all  transferred  to  the  side  of  B. 
This  operation  may  go  on  iudefinitely. 

"  Now,  if,  on  the  side  of  A,  the  cylinder  is  closed  by  a 


448  THE  nOMESTTC  CALORTC  ENGINE.  chap.  xxxi. 

second  piston  (wliicli  we  may  still  call  A),  and  not  by  a 
fixed  cap,  both  pistons  being  movable,  tlie  same  succession 
of  occurrences  will  take  place,  only  modified  by  the  move- 
ments which  may  be  given  to  A.  If  C  and  A  both  move 
in  the  direction  of  A,  both  their  valves  will  open,  and  air 
from  the  exterior  of  the  cylinder  will  pass  throiigh  both 
into  the  space  between  B  and  C.  If  they  both  move  toward 
B,  but  C  faster  than  A,  then  air  will  enter  on  the  side  of 
A,  and  flow  out  on  the  side  of  B,  the  valve  C  only  remain- 
ing closed.  If  both  move  toward  A,  but  A  faster  than  C, 
air  will  still  enter  the  space  between  C  and  A,  while,  in 
less  quantity,  it  is  passing  through  C  into  the  space  between 
C  and  B. 

"  Let  now  the  piston  A  be  supposed  to  occupy  a  posi- 
tion, say,  one-third  advanced  down  the  cylinder,  the  piston 
C  being  further  advanced  still,  and  let  the  valve  of  B  be 
secured  by  a  strong  sjDring  pressing  upon  it,  so  that  it  can- 
not be  opened  without  the  application  of  some  considerable 
force ;  and  in  these  circumstances  let  the  cylinder,  and 
consequently  the  air  contained  in  it,  be  heated.  The  elas- 
ticity of  the  confined  air,  being  increased  by  heat,  will  close 
the  valve  in  A,  and  that  piston  will  be  moved  in  the  direc- 
tion of  A,  until,  by  the  enlargement  of  volume,  the  elasticity 
shall  be  reduced  to  equality  with  that  of  the  external  air. 
If  the  heat  be  uniform  throughout  all  the  mass  of  confined 
air,  the  valve  in  C  will  be  equally  pressed  on  both  sides. 
Under  these  circumstances,  the  piston  C  could  be  moved 
toward    A,  if  there  were  any  means  of  acting  upon  it,   the 


CUAP.  XXXI.  THE  DOMESTIC  CALOBIC  EXaiXE.  449 

air  passing  tlirougli  the  valve  toward  B.  Bnt  if  au  attemjit 
were  made  to  move  the  pistou  itself  toward  B,  it  would 
encounter  resistance,  because  its  own  valve  would  be  closed 
by  the  movement,  and  the  valve  of  B  is  supposed  to  be 
forcibly  held  down.  Since  now  the  external  piston  must 
move  in  the  direction  A,  it  is  only  necessary  that  it  should 
be  propei-ly  connected  with  a  machine,  in  order  that  the 
force  exerted  by  the  heated  and  expanding  air  may  be  turned 
to  some  practical  account. 

"  If,  ao-aiu,  at  the  end  of  the  movement  the  air  could  be 
immediately  cooled  without  being  discharged,  the  heat  could 
be  again  applied  and  the  effort  repeated.  But  this  not 
being  practicable,  the  heated  air  may  be  allowed  to  escape 
by  relieving  the  valve  B  of  the  pressure  of  the  spring  which 
confines  it,  and  by  causing  the  piston  C  to  descend  to  the 
extremity  B  of  the  cylinder.  This  movement  of  C  not  only 
drives  out  the  hot  air,  but  it  draws  in  through  A  a  fresh 
supply  of  cold  air ;  and  if  A  descends  simultaneously  to  the 
position  originally  supposed — i.e.,  one-third  advanced  toward 
B — there  will  be  a  body  of  air  filling  the  other  two-thirds 
of  the  cylinder  at  the  common  temperature,  ready  to  be 
acted  on  anew  by  heat. 

"  In  this  statement  is  embraced  the  general  principle  of  the 
Ericsson  engine.  What  remains  is  to  explain  the  mechanical 
contrivances  by  which  the  movements  of  the  pistons  are 
governed,  and  to  describe  the  heating  apparatus  which  is 
employed  to  effect  the  prompt  dilatation  of  the  aii-.  Inas- 
much as  the  piston  which  we  have  called  C  is  shut  up  in 


450  THE  DOMESTIC  CALOBIC  ENGINE.  chap.  XXXI. 

the  cylinder  beliliul  A,  it  is  necessary  that  the  rods  which 
give  it  motion  should  pass  through  A.  They  do  so,  being- 
packed  by  means  of  stuffing-boxes  to  prevent  leakage;  and 
are  connected  at  their  external  extremities  with  oscillating 
levers  turning  on  a  fixed  centre  of  motion  at  their  extremi- 
ties, and  kept  in  motion  by  the  engine.  The  rod  of  the 
external  piston  A,  which  is  the  driving-piston,  is  also  con- 
nected with  an  upright  oscillating  lever,  turning  on  an  axis 
of  motion  at  its  lower  extremity,  and  carrying  at  its  upper  a 
horizontal  connecting-rod,  which  acts  on  the  crank  of  the  main 
shaft  of  the  engine.  It  would  be  simpler  to  connect  the  piston 
directly  with  this  crank ;  biit  if  that  mode  of  connection 
were  adopted,  the  stroke  of  the  piston  would  have  to  take 
place  in  both  directions,  forward  and  back,  in  equal  times. 
This  condition  is  not  favorable  to  the  action  of  the  machine ; 
and  inequality  in  this  respect  is  still  more  important  in  the 
case  of  the  supply-piston.  The  peculiar  ingenuity  of  this 
machine  is  in  fact  manifested  most  signally  at  this  point. 
By  means  of  the  systems  of  levers  interposed  between  the 
pistons  and  the  main  shaft,  provision  is  made  for  the  per- 
fect uniformity  of  the  revolution  of  the  shaft,  while  the 
pistons,  on  the  other  hand,  are  accelerated  and  retarded  in 
such  a  manner  as  to  fulfil  the  condition  that  the  aspiration 
of  the  charge  of  air  should  occupy  the  minimum  of  time. 
The  oscillating  levers  which  connect  Avith  the  piston-rods  of 
the  stipply-piston  are  kept  in  oscillation  by  crank-motion 
from  the  main  shaft,  and  in  their  oscillations  they  displace 
the  inner  piston,  encountering  no  resistance  but  friction.     In 


CHAP.  xxxr.  THE  DOMESTIC  CAUWIV  EXGIXE.  461 

consequence  of  tlie  un-unifoiin  ;uul  unequal  velocities  of  the 
two  i;)istons,  and  their  intentional  adjustment,  so  that  they 
do  not  begin  and  end  tlieir  course  together,  the  distance 
between  them  varies  in  a  manner  which  is  quite  important: 
first,  to  the  aspiration  of  the  charge ;  and  secondly,  to  the 
effectual  exposure  of  the  aspired  air  to  the  action  of  the 
furnace. 

"  It  is  of  coui-se  of  the  highest  importance  that  the  posi- 
tions of  tlie  cranks  on  the  main  shaft,  and  those  of  the 
axes  of  motion  of  the  oscillating  levers,  should  be  so  related 
to  each  other  as  to  produce  a  rapid  separation  of  the  two 
pistons  at  the  beginning  of  the  negative  stroke;  because  this 
is  the  time  when  the  aspiration  of  the  charge  must  take 
place.  During  this  time,  the  inner  piston,  gaining  on  the 
outer,  will  not  only  draw  in  the  fresh  charge,  but  it  will 
expel  the  exhausted  one;  the  escape-valve  being  lifted  foi- 
the  purpose  and  kept  raised  during  all  the  period  of  aspira- 
ti(in  by  means  of  a  cam.  When  the  pistons  are  at  the 
maximum  distance  from  each  otlier.  the  as])iration  is  ended. 
From  this  time  until  tlie  half  revolution  is  complete,  the 
confined  air  undergoes  compression,  and  the  movement  is 
maintained  by  the  fly-wlieel.  In  the  second  half  revolution 
the  driving-piston  is  urged  by  the  elasticity  of  the  air 
whicli  is  exalted  both  by  conqiression  and  by  heat. 

"  The  heating  is  accomplished  as  follows :  The  furnace  is 
within  the  cylinder,  at  the  end  which  we  have  called  B, 
where  the  cylinder  is  prolonged  to  receive  it.  It  is  of  iron, 
and    is    cylindrical    also,    a   small    annular   space    only    inter- 


452  THE  DOMESTIC  CALOBIO  ENGINE.  chap.  xxxi. 

vening  between  its  Avails  and  those  of  the  cylinder.  This 
space  is  open  to  the  interior,  but  is  closed  at  the  extreme 
end  ;  so  that  it  forms,  in  fact,  a  portion  of  the  proper  air- 
chamber.  To  the  supply-piston  C  is  attached  by  its  crown  a 
sheet-iron  cylindrical  bell,  which  enters  the  annular  space  Just 
spoken  of  without  touching  the  walls  of  the  furnace  or  those 
of  the  surrounding  cylinder.  The  valve  in  C  opens  above 
the  crown  of  this  bell ;  but  any  air  which  comes  through 
the  valve  from  the  side  of  A  can  only  reach  the  interior  by 
passing  down  the  annular  space  between  tlie  bell  and  the 
cylinder  Avail,  and  returning  up  the  annular  space  between 
the  bell  and  the  wall  of  the  furnace.  In  making  this  pas- 
sage, it  Avill  be  exposed  in  a  very  thin  sheet  to  the  action 
of  the  furnace  heat,  a  very  large  proportion  of  the  molecules 
being  brought  into  direct  contact  with  the  heated  iron. 

"  That  we  may  understand  how  this  movement  of  the  air 
is  made  forcibly  necessary,  we  need  only  consider  the  rela- 
tive movements  of  the  pistons  during  the  period  of  a  com- 
plete revolution.  At  the  beginning  of  the  negative  stroke, 
or  of  the  movement  of  A  in  the  direction  of  B,  the  supply- 
piston  takes  the  lead,  air  enters  through  the  valve  of  A, 
and  the  asioiration  is  soon  complete.  The  distance  between 
the  two  pistons,  which  determines  the  amount  of  aspiration, 
is  now  of  course  at  its  maximum.  A  next  begins  to  gain 
on  C,  but  both  movements  have  still  for  a  short  time  the 
same  (negative)  direction.  The  space  occujDied  by  the  air 
is  gradually  reduced;  or,  in  other  words,  the  air  undergoes 
compression.     The   piston   C  reaches   the  limit  of   its  course 


CHAP.  XXXI.  THE   DOMEHTIC  CALOBIC  LXGIXE.  453 

sooner  than  A.  It  begins  to  move  in  the  positive  direction, 
while  the  motion  of  A  is  still  negative.  The  valve  in  C  is 
opened  by  the  pressure,  the  air  passes  through,  and,  having 
no  other  channel,  descends  the  aiuiular  space  outside  of  the 
bell,  and  returns  by  the  annular  space  inside  the  bell,  becom- 
ing heated,  as  above  described,  in  its  progress.  Presently 
after  this  displacement  coniniences,  the  piston  A  also  reaches 
its  limit  of  movement,  and  the  direction  of  its  motion  becomes 
positive.  But  C  moves  the  faster  of  the  two,  so  that  the 
displacement  continues  throughout  the  greater  part  of  the 
positive  stroke.  A  little  before  the  eiul,  the  distance  between 
the  two  pistons  becomes  minimum,  and  they  are  then  nearly 
in  contact.  ^Tien  the  revolution  is  quite  complete,  this  dis- 
tance is  slightly  increased.  Just  before  this  time  C  will 
have  recommenced  its  negative  movement,  Avhile  A  continues 
still  to  be  moving  in  the  positive  direction. 

"  The  relative  movements  here  described  will  be  more  ad- 
vantageously compared  by  presenting  them  in  tabular  form, 
which  we  are  enabled  to  do  by  the  help  of  the  determinations 
made  by  Mr.  Mastaing,  of  Paris,  upon  the  Ericsson  engine, 
which  was  made  the  subject  of  experiment  in  1861  at  the 
Conservatoire  des  Arts  et  Metiers,  by  Mr.  Tresca,  sub-director 
of  that  institution.  In  the  first  column  of  this  table  are 
placed  the  angular  positions  of  the  driving-crank  on  the 
main  shaft  at  different  periods  of  the  revolution;  putting 
zero  to  rejiresent  the  position  of  the  craidv  when  the  piston 
A  is  about  to  commence  its  negative  stroke.  The  second 
column  gives   the  direction  of  motion   of   the   driving-piston, 


454 


TEE  DOMESTIC  CALOEIC  ENGINE. 


CHAP.  XXXI. 


and  its  motion  relative  to  that  of  tlie  other ;  and  the  third 
column  gives  the  same  particulars  in  regard  to  the  supply- 
piston.  The  last  column  gives  the  variation  of  distance  taking 
place  bet^veen  the  two  pistons  at  the  several  points  indicated 
in  the  table. 


Angular  posi- 
tion of  the 
cranli. 

Relative  motion  of  the  pistons. 

Distance 

between  the 

pistons. 

Driving-piston. 

Supply-piston. 

Degs. 

Oto    70 

Negative,  losing . .  . 

Negative,  gaining . . 

Increasing. 

70 

Negative,  equal. . . 

Negative,  equal . . . 

Maximum. 

70  to  120 

Negative,  gaining. . 

Negative,  lo.sing.  . . 

Decreasing. 

120 

Negative,  gaining. . 

Limit  of  course .... 

Decreasing. 

120  to  170 

Negative,  contrary. 

Positive,  contrary. 

Decreasing. 

170 

Limit  of  course .... 

Positive,  gaining.  . 

Decreasing. 

170  to  310 

Positive,  losing. . . . 

Positive,  gaining.. 

Decreasing. 

310 

Positive,  losing. . . . 

Positive,  gaining. . 

Minimum. 

310  to  340 

Positive,  gaining . . 

Positive,  losing. .  . . 

Increasing. 

340 

Positive,  gaining . . 

Limit  of  course .... 

Increasing. 

340  to  360 

Positive,  contrary . 

Negative,  contrary. 

Increasing. 

"  It  will  be  seen  that  the  negative  stroke  is  completed  in 
less  than  half  a  revolution  foi'  either  piston,  while  the  posi- 
tive stroke  requires  more ;  also,  that  this  inequality  is  con- 
siderably greater  for  the  supply-piston  than  for  the  driving- 
piston.  In  the  case  of  the  di'iving-piston  the  inequality  is 
as  170  to  190  deg. ;  in  that  of  the  supply-piston,  as  IGO  to 
200  deg.  These  inequalities,  which  could  not  exist  if  the  con- 
nection between  the  main  shaft  and  the  pistons  were  made 
directly,  as  in  the  steam-engine,  are  the  effect  of  the  interme- 


CHAP.  XXXI.  THE  DOMESTIC  CALoh'JC  EXGiyE.  455 

diate  system  of  levers,  aud  arc  iutentionally  produced.  The 
increase  of  distance  betAveeii  the  pistons  from  310  deg.  to 
the  end  of  the  revolution  is  not  an  advantage,  but  it  is  not 
a  great  increase,  the  total  distance  amounting  finally  only  to 
about  the  one-sixth  part  of  the  maximum  sepai-atiou,  and  re- 
ceiving the  principal  accession  to  its  amount  between  350  and 
3G0  deg.  As,  after  the  second  reversal  of  the  niovemeut  of 
the  supply-piston,  the  effective  power  of  the  engine  is  neces- 
sarily paialyzed,  the  escape  valve  is  opened  at  344  deg.  by  the 
action  of  the  cam  above  spoken  of,  and  the  aspiration  com- 
mences before  the  revolution  is  quite  complete.  The  valve 
is  closed  again  at  09  deg.,  just  as  the  aspiration  is  becoming 
maximum. 

"Inasmuch  as  the  effective  pt)wer  of  this  engine  is  negative 
or  zero  from  344  deg.  onward  to  170  deg.,  or  through  a  little 
more  than  half  a  revolution,  it  is  necessary  that  the  machine 
should  be  provided  witli  a  heavy  fl}-wheel  to  maintain  the 
movement  during  these  intervals.  Tlie  tl3•-^vheel  is  made  to 
act  also  as  a  sort  of  counterweight,  as  well  as  by  means  of 
its  moment  of  rotation,  the  side  of  the  wheel  which  is  de- 
scending during  the  peiiod  of  paralysis  being  made  consider- 
ably heavier  than  the  other.  A  companion  engine,  to  act 
positively  during  tlie  inaction  of  the  first,  would  render  such 
an  exjtedient  unnecessary ;  but,  unfortunately,  the  bulk  is 
considerable  relatively  to  the  power,  and  it  would,  in  gen- 
eral, be  a  disadvantage  to  double   it. 

"  The  engines  of  Ericsson  are  largely  in  use  in  the  United 
States,  but    as   yet   they  have  not  been  constructed  of   any 


456  THE  DOMESTIC  CALORIC  ENGINE.  chap.  xxxi. 

considerable  power.  As  a  general  rule,  tliey  fall  within 
three  or  four  liorse-power  as  an  outer  limit,  tliouyli  it  is  be- 
lieved that  there  have  been  made  some  exceeding  this  limit. 
On  account  of  their  safety  and  convenience  they  have  been 
regarded  with  favor ;  and  it  has  been  claimed  for  them  as  an 
additional  recommendation  that  they  are  economical.  Such 
did  not  appear  to  be  the  fact  in  the  case  of  the  particular 
engine  which  was  the  subject  of  the  experiments  of  Mr. 
Tresca  above  referred  to.  In  this  machine,  which  was  of 
two  horse-power,  the  result  of  very  careful  ti'ial  showed  a 
consumption  of  4.13  kilograms  (about  nine  pounds)  of  coal 
per  horse-power  per  hour.  ■•'  In  comparison  with  steam,  this 
cannot  be  called  a  large  economy.  The  consumption  of  a 
good  steam-engine  ought  not  to  exceed,  per  horse-power  per 
hour,  two  kilograms  at  the  outside.  One  and  a  half  ought 
to  suffice. 

"It  may  be  observed,  in  conclusion,  that  Ericsson  makes 
no  attempt  to  carry  the  temperature  in  this  engine  to  a  very 
high  point.  The  mean  maximum  temperature  in  the  experi- 
ments at  the  Conservatoire  did  not  exceed  270°  Fahrenheit, 
though  doubtless  portions  of  the  air  received  a  greater  de- 
gree of  heat  than  this.  The  expansion  of  volume  was  further 
determined  to  be  but  as  1  :  1.48 — that  is  to  say,  about  fifty 
per  cent,  of  the  original  bulk. 

*  There  is  not  a  single  instance  on  record  in  the  United  States  in  which  the  con- 
sumption has  exceeded  four  pounds  of  anthracite  coal  an  hour  per  horse-power.  It 
should  be  observed,  however,  that  by  forcing  the  combustion  by  an  excess  of  fuel,  put 
into  the  furnace  under  an  imperfect  draught,  the  consumption  may  be  more  than 
doubled. 


CUAI'.  XXXI.  THE  DOMESTIC  CALORIC  ENGINE.  457 

"  The  general  description  here  given  will  be  made  more 
intelligible  by  reference  to  the  figures  of  the  engine  given 
in  Plate  46. 

"  Of  the  two  pistons  shown  at  A  and  F,  the  first,  A,  is 
the  driving-piston,  and  the  second  the  supply-piston,  which 
in  the  foregoing  explanation  we  have  called  C.  In  A  is 
seen  a  valve  marked  a. 

"  At  B  is  an  axis  of  motion,  the  office  of  which  is  to  com- 
municate movement  to  the  piston  A,  by  means  of  a  crank  o, 
a  connecting-rod  p,  a  second  crank  q,  and  another  rod  /■. 

"  In  the  piston  F  the  valve  of  communication  is  sliown  at 
f.  The  solid  portion  F'  is  filled  with  plaster,  or  other  badly- 
conducting  substance,  while  F"  marks  the  bell-shaped  pro- 
longation which  extends  into  the  annular  space  surrounding 
the  furnace.  A\"lien,  l^y  the  approach  of  the  piston  F  to  the 
piston  A,  the  space  between  these  two  pistons  is  reduced, 
there  is  no  escape  for  the  air  between  them  but  that  which 
is  afforded  by  the  annular  cavities  between  this  bell  and  the 
external  wall  of  the  machine  /',  on  the  one  IkuuI,  and  the 
wall  of  the  fuinace  itself  on  the  other.  The  air  passes  first 
along  the  outer  space  to  the  mouth  of  the  bell,  and  returns 
thi'ough  the  inner,  forming  a  thin  stratum  in  immediate  con- 
tact witli  the  hot  wall  of  the  furnace. 

"  Another  axis  of  motion  is  shown  at  C,  of  which  it  is 
the  office  to  communicate  movement  to  the  sujiply-piston  F, 
through  the  crank  o,  the  connecting-roti  s,  and  the  cranks  i 
and  ",  which  last  two  are  fixed  to  the  arbor  C,  at  a  fixed 
anirle  to  each  other  of  seven  detirees. 


458  THE  DOMESTIC  CALOBIC  ENGINE.  chap.  xxxi. 

"  The  escape-valve  is  placed  at  D,  and  kept  iu  position 
l)y  the  spring  d.  A  cam  D',  acting  on  this  valve  through  the 
lever  D",  opens  it  Just  before  the  driving-piston  commences 
its  descent  at  the  end  of  the  positive  stroke. 

"  The  furnace  is  enclosed  in  the  iron  box  G,  the  grate- 
bars  being  shown  at  g.  G'  indicates  plates  of  iron  designed 
to  protect  the  walls  of  the  fni'nace. 

"  In  order  to  bring  the  two  j)istons  into  a  favorable  posi- 
tion for  starting,  the  fly-wheel  is  turned  on  its  axis ;  and, 
for  the  purpose  of  facilitating  this  operation,  the  ai'bor  K 
is  introduced,  which  enables  the  attendant  to  act  on  the  fly 
by  means  of  the  clicks  marked  Ic,  and  the  notches  h'. 

"  The  furnace-door  I  is  made  double  to  reduce  loss  by  radi- 
ation. The  walls  of  the  furnace  are  similarly  protected  by 
means  of  a  double  envelope. 

"  The  products  of  combustion  escape  from  the  furnace 
through  the  flues  li,  protected  by  fire-brick,  and  are  carried 
oft'  by  the  chimney  H." 

The  caloric  engine  thus  described  was  patented  1858,  the 
Rumford  medal  being  awarded  in  1862  for  its  successful 
practical  application. 

The  following  address  by  Professor  Horsford,  on  present- 
ing the  medal,  cannot  properly  be  omitted  in  this  ^vork  : 

"  At  the  time  the  vote  of  the  American  Academy  of 
Arts  and  Sciences  conferring  upon  you  the  Eumford  Pre- 
mium was  passed,  I  had  the  honor  to  be  Chairman  of  the 
Rumford  Committee,  and,  you  will  remember,  signified  my 
wish  to  relieve  myself  of  the  trust  imposed  upon  me  ;    but, 


CHAP.  XXXI.  THE  DOMESTIC  CALORIC  EXGINE.  459 

as  this  formal  act  aud  tlie  simple  cerumouy  appropriate  to 
it  have  been  postponed  in  consequence  of  the  pressure  of 
the  war,  in  which  you,  sii-,  have  borne  so  conspicuous  a  part, 
the  custody  of  the  vote  and  medal  has  been  continued  w  ith 
me  to  the  present  time. 

"1  have  the  honor  now  to  place  in  your  hands  a  certi- 
fied copy  of  the  vote  passed  by  the  Academy  at  its  annual 
meeting,  June  10,  1862.     It  is  jis  follows: 

"  '  Voted,  That  the  Rumford  Premium  be  awarded  to 
John  Ericsson,  for  his  improvements  in  the  management  of 
heat,  particularly  as  shown  in  his  caloric  eugine  of  1858.' 

"  In  now  handing  to  you  the  gold  and  silver  medals 
which  have  been  prepared  in  accordance  with  the  statutes 
of  the  Academy,  I  beg  to  congratulate  you  upon  the  honors 
you  have  ^von  through  a  life  of  research  and  experiment,  de- 
voted to  the  promotion  of  the  prosperity  and  well-being  of 
mankind,  in  the  field  contemplated  by  the  illustrious  founder 
of  the  Rumford   Premium."* 

*  A  patent  was  granted  June  15,  1809,  to  a  German  engineer,  tor  a  machine 
actuated  by  heated  air,  identical  in  principle  and  mechanical  combination  with  my 
caloric  engine  of  1858,  the  only  difference  being  that,  like  the  solar  engine  delineated 
on  Plate  07,  aud  other  air-engines  constructed  by  me  in  the  United  States  at  various 
times — as  far  back  as  IS-tJ — the  patented  engine  uses  the  same  air  over  and  over. 
The  patent  refen-ed  to  also  embraces  a  supposed  novel  plan  of  applying  a  water- 
chamber  round  the  open  end  of  the  cylinder  for  cooling  the  same.  Now,  the  leading 
feature  of  a  large  caloric  engine  built  by  me  at  the  Delaraater  Iron-Works,  in  Xew 
York,  185f>,  was  that  of  cooling  the  open  end  of  the  cylinder  by  such  a  wnter- 
chambcr.  The  patented  engine,  therefore,  is  a  flagrant  plagiarism  on  devices  already 
carried  into  practice. 


CHAPTER   XXXIL 

THE  MONITOR  SYSTEM  OP  IRON-CLADS. 

(SEE   PLATES   47   AND    48.) 


The  monitor  system  is  thus  noticed  in  J.  Scott  Russell's 
great  work  on  Naval  Architecture  : 

"It  is  a  creation  altogether  original,  peculiarly  American, 
admirably  adapted  to  the  special  purpose  which  gave  it 
birth.  Like  most  American  inventions,  use  has  been  al- 
lowed to  dictate  terms  of  constriiction,  and  purpose,  not 
prejudice,  has  been  allowed  to  rule  invention. 

"The  I'uling  conditions  of  construction  for  the  inventor 
of  the  American  fleet  were  these :  the  vessels  must '  be  per- 
fectly shot-proof,  thej'  must  fight  in  shallow  water,  they 
must  be  able  to  endure  a  heavy  sea,  and  pass  through  it, 
if  not  fight  in  it. 

"The  American  iron-clad  navy  is  a  child  of  these  con- 
ditions. Minimum  draught  of  water  means  minimum  extent 
of    sui-face,    protected    by    armor ;    perfect   protection    means 

460 


CHAP.  XXXII.         TEE  MONITOR  SYSTEM  OF  lEOX-CLADS.  461 

thickness  to  resist  the  heaviest  shot,  and  protection  for  the 
\\hole  length  of  the  ship;  it  also  means  pei-fect  protection 
to  guns  and  gunners.  Had  they  added  \vhat  our  legislators 
exact — that  the  ports  shall  lie  in  the  ship's  side,  nine  feet 
above  the  water — the  problem  might  at  once  have  l)ecome 
impossible  and  absurd  ;  but  they  wanted  the  work  done  as 
it  could  be  done,  and  allowed  tlie  conditions  of  success  to 
rule  the  methods  of  construction. 

"The  conditions  of  success  in  the  given  circumstances 
wei-e  these:  that  you  slu)uld  not  require  the  sides  of  the 
ship  to  rise  much  above  the  water's  edge  ;  that  you  should 
not  require  more  protection  to  the  guns  than  would  contain 
guns  and  gunners ;  that  you  should  be  content  with  as  many 
guns  as  the  ship  could  carry,  and  no  more. 

"To  do  the  work,  thereft)re,  the  full  thickness  of  armor 
required  to  keep  out  the  enemy's  shot  was  taken,  but  the 
ship  was  made  to  rise  a  feAv  inches  above  watei-,  and  no 
more  ;  and  so  a  narro\v  stiip  of  thick  armor,  all  along  the 
upper  edge  of  the  ship's  side,  gave  her  complete  protection. 
Thus  the  least  quantity  of  thickest  armor  did  most  work 
in  protecting  the  ship,  engines,  boilers,  and  magazine.  Next, 
to  protect  the  guns,  a  small  circular  fortress,  shield,  or  tower 
ciK'ircled  a  couple  of  guns,  and,  if  four  guns  were  to  be  car- 
ried, two  such  turrets  carried  the  armament  and  contained 
the  gunners.  Thus,  again,  weight  of  annor  was  spared  to 
the  utmost,  and  so  both  ship  and  armament  were  completely 
protected. 

"  But  the  consequences    of   these    conditions  are  such  as 


462  THE  MONITOR  STSTEM  OF  IROK-CLABS.        chap,  xxxii. 

we,  at  least  for  sea-going  ships,  would  reluctantly  accept. 
The  low  ship's  side  will,  in  a  sea-way,  allow  the  sea  to 
sweep  over  the  ship,  and  the  waves,  not  the  sailors,  will 
have  possession  of  the  deck.  The  American  accepts  the 
conditions,  removes  the  sailors  from  the  deck,  allows  the 
sea  to  have  its  way,  and  drives  his  vessel  through,  not  over, 
the  sea  to  her  fighting  destination,  by  steam,  abandoning 
sails.  The  American  also  cheei-fully  accepts  the  small  round 
turret  as  protection  for  guns  and  men  ;  and  pivots  them  on 
a  central  turn-table  in  the  middle  of  his  ship,  raising  his 
port  high  enough  to  be  out  of  the  water,  and  then  fighting 
his  gun  through  an  aperture  little  larger  than  its  muzzle. 

"By  thus  frankly  accepting  the  conditions  he  could  not 
control,  the  American  did  his  work  and  built  his  fleet.  It 
is  beyond  doubt  that  the  American  Monitor  class,  with  two 
turrets  in  each  ship,  and  two  guns  in  each  turret,  is  a  kind 
of  vessel  that  can  be  made  fast,  shot-proof  and  sea-proof.  It 
may  be  uncomfoiiable,  but  it  can  be  made  secure.  The  sea 
may  possess  its  deck,  but  in  the  air,  above  the  sea,  the 
American  raises  a  platform  on  the  level  of  the  top  of  his 
turrets,  which  he  calls  his  hurricane  deck,  whence  he  can 
look  down  with  indifference  at  the  waves  fraitlessly  foam- 
ino-  and  breaking  themselves  on  the  abandoned  deck  below. 
His  vessel,  too,  has  the  advantage,  as  he  thinks  it,  of  not 
rolling  with  the  waves ;  so  that  he  can  take  his  aim  steadily 
and  throw  his  shot  surely.  Thus,  if  he  abandons  much  that 
we  value,  he  secures  what  he  values  more. 

''  I  think  I  have  reason  to  know  that  the  American  turret 


cJiAr.  xxxu.        TRE  MOMTOIi  UlSrEM  OF  lEOS-CLADS.  463 

ships,  of  the  larger  class,  with  two  turrets  and  four  guns, 
are  successful  vessels — successful  beyond  the  measure  of  our 
English  estimate  of  their  success.  Like  so  luauy  American 
inventions,  they  are  severely  subject  to  the  conditions  of 
use,  and  successful  by  the  rigidity  and  precision  with  which 
they  fit  the  end  and  fulfil  the  purpose  which  was  their  aim. 

"Plate  47  contains  side  elevation,  deck  plans,  and  cross- 
section  of  the  original  American  Monitor  of  Caj)tain  Ericsson 
— the  first  turret  ship  that  distinguished  herself  in  action, 
having  to  engage  with  her  single  turret  and  pair  of  guns  a 
large  broadside  ship  of  much  lieavier  tonnage  and  armament, 
which  she  thoroughly  defeated. 

''  Captain  Ericsson,  the  builder  of  the  Monitor,  has  long 
been  distinguished  equally  in  England  and  America.  He 
was  known  as  the  builder  and  designer  of  one  of  the  most 
remarkable  engines,  in  the  original  competition,  preliminary 
to  the  opening  of  the  Liverpool  and  Manchester  Railroad; 
he  was  afterwards  distinguished  in  the  introduction  of  the 
screw-propeller  in  steam  navigation ;  and  he  has  crowned  his 
career  by  the  successful  construction  of  the  class  of  turret 
ships,  which  appear  to  have  been  taken  up  with  avidity,  and 
prosecuted  with  energy,  by  the  American  Government ;  and 
during  the  coui-se  of  their  sad  civil  w.ir  the  'monitors'  appear 
to  have  rendered  to  the  Federal  side  very  important  services. 
The  design  of  these  vessels  has  about  it  all  the  character- 
istics of  American  audacity.  Every  conventionality  of  the 
ship  has  been  despised  and  di.scarded  ;  in  the  sailor's  sense 
of  the  word,  there  is  nothing  'sliijKshaiie '  about  this  original 


4C4  THE  MONITOE  SYSTEM  OF  IBON-CLABS.       ouap.  xxxii. 

Ilonitor ;  e\'ery thing  is  unusual.  She  has  neither  keel,  nor 
bilges,  nor  bulwarks.  She  is  very  nearly  a  London  bridge, 
covered  by  a  great  horizontal  platform  of  timber,  projecting 
Ijeyoud  her  deck,  and  descending  below  the  \vater-line.  This 
great  upper  platform  in  no  way  conforms  to  the  shape  of 
the  under-ship  which  carries  it ;  it  is  obviously  meant  to 
shelter  the  rudder  and  the  stern  from  every  attempt  to 
damage  them  by  collision.  At  the  bow  the  entire  hull  is 
equally  protected  by  the  overhanging  platform  of  the  deck, 
and  the  whole  upper  works  of  the  ship  are  covered  with 
thick  iron  armor  on  both  sides,  and  the  wooden  deck  is  pro- 
tected by  iron  plates.  The  rudder  is  a  balanced  rudder,  and 
the  ship  is  propelled  by  a  single  screw ;  the  boilers  are  the 
double-tier  boilers,  of  the  ordinary  construction,  with  four 
sets  of  flues.  It  will  be  noticed  that  the  arrangements  of 
the  turret  are  very  different  from  Ca2)tain  Coles's  arrange- 
ments. The  whole  turret  is  on  the  upper  deck,  exposed  to 
shot ;  it  is  not  carried  on  a  revolving  set  of  rollers,  but  is 
pivoted  on  the  centre,  which  seems  to  carry  most  of  its 
weight  by  means  of  an  iron  trussing,  from  ^vllich  it  is,  as  it 
were,  suspended,  and  it  slides  on  a  smooth  metal  plate  lying 
on  the  deck.  The  turret  is  worked  by  a  small  pair  of  donkey 
engines,  working  on  tooth  gear,  and  the  ports  are  covered 
by  hanging  blocks.  Like  our  turret,*  the  Monitor  shield  has 
two  guns  worked  parallel  to  each  other  on  slides.     The  man- 

*  The  English,  in  abandoning  the  cupola  of  Coles,  and  copying  the  monitor 
turret,  also  adopted  the  term  turret.  For  some  time,  however,  the  English  naval 
architects  adhered  to  the  word  cupola  ;  but  in  a  short  while  the  phrase  cupola  was 
dropped,  hence  "turret  ship''  in  place  of  "cupola  ship." 


CUAP.  XXXII.         THE  MO.MTOR  SiHTEM  OF  IL-OX-CLADS.  4(55 

ner  in  wliich  these  turrets  were  afterwards  improved  and 
matured  by  experience  is  shown  in  Plate  49,  and  it  is  certain 
that  Captain  Ericsson  rendered  great  service  to  liis  country 
by  inventing  at  once,  and  successfully  introducing,  a  class 
of  vessels  peculiarly  suited  to  action  in  their  inland  waters 
and  sluillo\v  navigations  ;  and  when  we  consider  the  extreme 
rapidity  which  attended  the  execution  of  the  project,  we 
must  say  that  the  original  Monitor  was  a  remarkable  success, 
:ind  that  she  was  a  type  of  an  entirely  new  class  of  war- 
shi[i." 

The  origin  of  the  name  "  monitor  "  calls  for  an  explana- 
tion in  this  place.  The  Navy  Department  at  "Washington 
having,  shortly  before  the  launch,  requested  me  to  suggest 
an  appropriate  name  for  the  impregnable  turreted  steam- 
battery,  I  addressed  a  letter  to  the  Assistant  Secretary  of 
the  Navy,  sajing :  " The  impregnable  and  aggressive  char- 
acter of  this  structure  will  admonish  the  leaders  of  the 
Southern  Rebellion  that  the  batteries  on  the  Ijaiiks  of  their 
rivers  will  no  longer  pi'esent  barriers  to  the  entrance  v{  the 
Union  forces. 

"The  iron-clad  intruder  will  thus  prove  a  severe  monitor 
to  those  leaders.  But  tliere  are  other  leaders  who  Avill  also 
be  startU'd  and  admonished  by  the  booming  of  the  guns  from 
the  impregnable  iron  turret.  'Downing  Stieet  '  will  hardly 
view  with  indifference  this  last  '  Yankee  notion,'  this  monitor. 
To  the  Lords  of  the  Admiralty  the  new  craft  will  be  a 
monitor,  suggesting  doubts  as  to  the  propriety  of  completing 
those  four  steel  ships  at  three  and  a  half  millions  apiece. 


466  TKE  MONITOB  SYSTEM  OF  IliON-CLABS.       CHAP.  XXXil. 

"  On  these  and  many  similar  grounds  I  propose  to  name 
tlie  new  battery  Monitor.'''' 

It  Avill  be  recollected  that  this  letter  was  regarded  in 
England  as  possessing  political  significance,  several  membei'S 
of  Parliament  having  called  for  its  reading  in  the  House  of 
Commons  when  the  news  of  the  result  of  the  battle  between 
the  Monitor  and  the  Merrimack  appeared  in  the  Times. 
Uufpiestionably,  the  advent  of  the  Monitor  materially  coun- 
teracted the  pressure  which  the  French  Emperor  bi'ought  to 
bear  on  the  British  Ministry  at  the  time,  in  favor  of  the 
Southern  States. 

John  Bourne,  the  greatest  authority  on  naval  engineering 
of  our  time,  in  a  critical  examination  of  the  monitor  system 
published  in  London,  1866,  observes  : 

"  The  confidence  of  the  Americans  in  the  shot-proof  quali- 
ties of  their  monitors  is  manifested  by  many  of  the  incidents 
of  the  late  Eebellion,  one  of  Avhich  is  that  Captain  Worden, 
of  the  monitor  Montcmlc,  attacked  and  destroyed  the  Con- 
federate vessel  Nashville,  w^hen  lying  under  the  guns  of  Fort 
McAllister,  in  Georgia ;  and,  although  the  fort  Avas  all  the 
time  pouring  a  fire  upon  the  monitor  from  its  heaviest  guns, 
the  monitor  took  no  notice  of  it,  but  proceeded  without 
interruption  to  the  destruction  of  her  antagonist.  Another 
neAV  feature  in  naval  war  is  that,  in  the  attack  on  Fort 
Fisher,  the  fire  of  the  rest  of  the  fleet  was  directed  against 
the  fort  over  the  monitors ;  and  although  shot  falling  short 
and  shells  prematurely  exploding  could  not  be  prevented  in 
such  an  engagement,  the  monitors,  it  was  felt,  M-ere  able  to 


CHAP.  XXXII.         THE  MOMTOi;  Sl'STFil  OF  IROS-CLADS. 


407 


encounter  such  risks  with  impunity.  The  monitors,  during 
two  years  of  active  service,  in  all  weathers,  on  a  hostile  and 
stomiy  coast — sometimes  Avatching  for  blockade-runners  in 
Cuba,  sometimes  engaged  in  the  Gulf  of  Mexico,  and  often 
at  sea  in  heavy  gales — were,  on  an  average,  each  twenty-five 
times  in  action :  being  a  larger  amount  of  service  than  that 
of  any  vessels  recorded  in  history.  Shot  could  not  damage 
them ;  storms  could  not  swamp  them ;  and  at  the  end  of 
the  war  they  wei-e  as  effective  as  at  the  beginning.  The 
following  extract  from  a  report  of  Admiral  Dahlgren  will 
show  something  of  the  kind  of  service  in  whicli  some  of 
the  monitors  were  employed  during  three  months  in  the 
summer  of  1863,  and  the  number  of  shots  they  fired  and 
witli  impunity  received  : 


Nftme  of  Monitor. 

No.  of  shots  fired. 

Hits. 

Hits  at 
Ogeechec. 

Total  hits 

received 

from 

the  enemy. 

15-inch. 

llinch. 

Catsldll 

Montauk 

Lehigh 

Passaic 

Naliant 

Patapsco  . . . 
"NYeehawken 
Nantucket . . 

IBS 
301 

41 
119 
170 
178 
264 

44 

425 
478 
28 
107 
276 
230 
633 
155 

86 
154 
36 
90 
09 
90 
134 
53 

20 
14 

35 
36 
47 
53 
51 

40 
9 

1 

106 
214 
30 
134 
105 
144 
187 
104 

1,255 

2,332 

718 

256 

56 

1,030 

Mr.  Bourne  also  presents  the  following  extracts  from  the 


468  THE  MONITOR  SYSTEM  OF  IBON-GLADS.        chap,  xxxir. 

reports  of  Captain  Jolm  Rodgers,  of  the  monitor  Weehatvkeii, 
to  the  Secretary  of  the  American  Navy : 

(1)  June  20,  1863. 

"  The  opinion  fc^rmed  then  confirmed  my  anticipations, 
that  a  hnll  rising  l)nt  little  above  the  surface  of  the  water 
(in  this  case  only  16  inches),  and  having  a  central  elevation, 
as  in  the  monitors,  is  the  sfcape  to  form  a  good  sea-boat ; 
and  I  am  convinced  that  on  this  idea  all  successful  iron-clads 
must  be  built.  This  form  reduces  the  surface  to  be  plated 
to  a  minimum,  and  puts -the  part  having  the  necessary  eleva- 
tion above  the  sea  for  fighting  guns  where  it  can  be  carried 
without  inconvenience,  and  in  the  Wechaivke/i  is  easily  carried. 
With  us,  I  think,  safety  is  solely  a  question  of  strength. 

"  I  had  relied  upon  former  experience  to  correct  any  faulty 
motion  which  I  might  discover  in  a  sea-way,  by  shifting  or 
reducing  weights.  I  abandoned,  however,  the  idea  of  improve- 
ment.    As  I  watched  the  action  of  the  vessel  it  was  perfect." 

(2)  July  22,   1863. 

"On  Thui'sday  night,  when  off  Chincoteague  Shoals,  ^ve 
had  a  severe  gale  from  east-northeast,  with  a  ver)-  heavy  sea, 
made  confused  and  dangerous  by  the  proximity  of  the  land. 
The  waves  I  measured  after  the  storm  abated.  I  found  them 
23  feet  high.  They  were  certainly  7  feet  higher  in  the 
midst  of  the  storm. 

"During  the  heaviest  of  the  gale  I  stood  upon  the  turret 
and  admired  the  behavior  of  the  vessel.  She  rose  and  fell 
to  the  waves,  and  I  concluded  then  that  the  monitor  form 
had  great  sea-going  qualities.     If   leaks   were  |)rc\-ented,   no 


ciiAi".  xxxii.      TUI-:  MoMToi:  iii:;sTJJM  of  muy-CLAUS.  409 

Imnioaue  could  injure  her.  1  presume  in  two  days  we  shall 
be  ready  for  aii}-  service,  as  we  ueed  uo  repaiis,  aud  ouly 
some  little  fittings." 

"  It  may  be  added,"  says  Mr.  Bourne,  "that,  on  the  occasion 
of  the  heavy  gale  which  occurred  just  before  the  attack  on 
Fort  Fisher,  the  nionitois  were  the  oidy  vessels  of  the  fleet 
which  were  able  to  ride  it  out  without  di'agging  their  anchors; 
aud  on  the  occasion  of  a  common  steamer  having  been  sent 
to  escort  a  monitor,  before  confidence  had  yet  been  established 
in  the  seawoi-thiness  of  tliat  class  of  vessel,  the  steamer,  hav- 
ing liroken  down  in  a  heavy  sea,  was  taken  in  tow  by  the 
monitor,  and  was  carried   by  her  safely  into  port." 

Mr.  Bourne,  in  proof  of  the  conifcirt  and  healthiness  of 
the  monitors,  likewise  presents  the  following  extract  from 
A  repoi-t  of  the  Secretary  of  the  United  States  Navy  to 
Congress : 

"It  is  gratifying  to  know  that  an  examination  of  the  sick 
reports,  covering  a  period  of  over  thiity  months,  shows  that 
so  far  from  being  unhealthy,  there  was  less  sickness  on  board 
the '  monitor  vessels  than  in  the  same  number  of  wooden 
.ships  with  an  e(pial  niiniber  of  men,  and  in  similarly  exposed 
positions.  The  exemjition  from  siekness  in  the  iron-dads  is 
in  some  instances  i'emarkal>le.  Thei'e  were  on  boaid  the 
SaiKjus,  from  NovemI)er  25,  1864,  to  April  1,  1805.  a  period 
of  over  four  months,  but  four  eases  of  sickness  (excluding 
accidental  injuries),  and  of  these  two  were  diseases  from 
which  the  patients  had  suflVred  for  years.  In  the  M(>iit<tril; 
for  a  period  of  <^ne  hundred  and  sixty-five  days  prior  to  May 


470  THE  MONITOR  SYSTEM  OF  IR0N-CLAD8.       chap,  xxxii. 

29,  1865,  there  was  but  one  case  of  disease  on  board.  Other 
vessels  exhibit  equally  remarkable  results,  and  the  conclu- 
sion is  reached  that  no  wooden  vessels  in  any  squadron 
throughout  the  world  can  show  an  equal  immunity  from 
disease.  The  facts  and  tables  presented  are  worthy  of  care- 
ful study." 

The  following  vote  of  thanks  was  passed  by  the  Thirty- 
seventh  Congress,  March  28,  18G2  : 

"  Resolved,  by  the  Senate  and  House  of  Kepresentatives 
of  the  United  States  of  America  in  Congress  assembled,  That 
it  is  fit  and  proper  that  a  public  acknowledgment  be  made 
to  Captain  John  Ericsson  for  the  enterprise,  skill,  energy,  and 
forecast  displayed  by  him  in  the  consti-uction  of  his  iron-clad 
boat,  the  Monitor,  which,  under  gallant  and  able  management, 
came  so  opportunely  to  the  rescue  of  our  fleet  in  Hampton 
Roads  and,  perchance,  of  all  our  coast  defences  near,  and 
arrested  the  work  of  destruction  then  being  successfully 
prosecuted  by  the  enemy  with  their  iron-clad  steamer,  seem- 
ingly irresistible  by  any  other  power  at  our  command ;  and 
that  the  thanks  of  Congress  are  hereby  presented  to  him 
for  the  great  service  which  he  has  thus  rendered  to  the 
country." 

It  will  be  proper  to  mention,  also,  that  several  iron-ship 
builders,  in  conjunction  \vith  the  proprietors  of  some  of  the 
most  important  marine-engine  establishments  on  the  Atlantic 
coast,  in  token  of  their  appreciation,  honored  me  by  present- 
ing a  model  of  the  Monitor,  weighing  upwards  of  fourteen 
pounds,  manufactured  of  pure  gold. 


CHAPTER  XXXIII. 

THE    MONITOR    TURRET    AND    THE    CENTENNIAL 
EXHIBITION. 

(SEE   PLATE   49.) 


The  imperfect  character  of  the  monitor  turret  exhibited 
in  Fairmount  Park  has  been  noticed  with  surprise  by  pro- 
fessional visitors.  In  view  of  the  important  results  attained 
by  the  adoption  of  this  structure  during  the  war,  it  cannot 
be  denied  that  a  painted  wooden  re^u'esentative  is  unworthy 
of  the  occasion.  Nor  need  it  be  urged  that  some  turret 
bearing  the  marks  of  actual  conflict  ought  to  have  been 
transferred  to  the  Exhiliition.  Experts  are  aware  tliat,  owing 
to  the  laminated  character  of  these  turrets,  they  may  readil}' 
be  taken  down,  and  the  plates  transported  and  put  up  at 
any  required  distance  from  the  vessel.  Besides,  it  may  be 
shown  that  this  process  would  have  been  less  expensive  than 
erecting  a  complete  representative  turret  and  mechanism. 
Regarding  the  armament   applied   within  the  wooden   turret, 


472  THE  MOXITOll   TUliBET.  chap,  xxxill. 

naval  artillerists  from  aljroad,  who  expected  to  have  had 
an  opportunity  of  examining  the  detail  of  the  friction-gear 
peculiar  to  the  mcinitor  armament,  have  been  greatly  dis- 
appointed to  find  that,  instead  of  the  carriages  on  which 
the  guns  wavQ  mounted  during  the  war,  an  experimental 
steam-carriage  devised  by  an  engineer  from  St.  Louis,  after 
the  war,  has  been  placed  in  the  representative  turret.  In 
consequence  of  this  misleading  procedure  on  the  2)art  of  the 
authorities,  of  excluding  the  carriages  which  had  been  used, 
the  majority  of  visitors  have  naturally  imagined  that  the 
monitor  guns,  during  the  war,  were  mounted  on  the  experi- 
mental carriage  referred  to."  It  should  be  mentioned  that 
the  plan  of  checking  the  recoil  of  our  guns  by  friction  has 
not  been  superseded  in  the  navy,  and  that  friction  gun- 
carriages  are  at  present  being  constructed  for  the  Navy 
Department  under  my  patents. 

THE    PILOT-TIOUSE. 

The  pilot-house — wheel-house — of  the  monitors,  and  the 
steering-gear  which  it  contains  (see  Plate  49),  forming  the 
most  important  features  of  the  system,  their  exclusion  from 
the  turret  at  the  Centennial  Exhibition  must  be  regarded  as 
an  untoward  circiimstance.  It  cannot  be  supposed  that  the 
otfieer  charged  with  the  duty  of  putting  up  the  i-epresenta- 
tive  turret  would  incur  the  responsibility  of  excluding  with- 
out authority  that  part  of  the  system  which  most  interests 

*  My  oari'iage,  operated  by  a  circular  compressor,  exhibited  in  the  wooden  tuiTet, 
was  applied  in  the  Dunderherg,  but  not  in  the  monitors  during  the  war. 


CHAP,  xxxill.  TIIK   MOMTOR   TURRET.  473 

the  professional  visitor.  The  country  is  aware  that  Adniiial 
Porter's  report  to  the  Seci'etary  of  the  Navy,  pultlished 
whiU-  the  prei)ai'ations  for  the  Centennial  Kxhiliitioii  were 
in  progress,  contained  a  reconiniendatiou  to  abolish  the  pilot- 
house of  the  monitor  turrets.  Possildy  this  recommendation, 
condenniatory  of  my  invention,  led  to  the  exclusion  of  the 
steering  machinery  and  the  massive  [li lot-house  from  the 
representative  turret  in  Fairmount  Park.  T  do  not  propose 
to  investigate  the  cause  which  has  led  to  the  exhibition  of 
my  invention  in  a  mutilated  state,  but  I  feel  called  upon 
to  show  that  the  I'emoval  of  the  pilot-house  from  the  turrets 
recommended  by  Admiral  Porter  is  highly  improper  and 
incompatible   with   the   monitor  system. 

Well-informed  naval  officers  are  aware  that  Worden  failed 
to  sink  the  MerrimacTc  at  IIami)ton  Roads  because  he  could 
not  personally  control  the  firing  and  at  the  same  time  direct 
the  steering  of  his  vessel  from  a  point  enabling  him  to  ob- 
serve properly  the  movement  of  his  antagonist.  This  fact 
was  well  understood  by  the  authorities  at  Washington,  the 
Assistant  Secretaiy  of  the  Navy  having  liimself  witnessed 
the  battle  and  the  ineffectual  firing.  I  was  accordingly  re- 
quested by  the  Navy  Department,  shortly  after  the  conflict, 
to  devise  some  means  of  steering  from  the  turret.  The  de- 
spatch conveying  this  request  contained  several  important 
suggestions,  and  closed  with  the  following  sentence :  "  The 
placing  the  wheel-house  cm  the  turi'et  woidd  double  the 
formidable  character  of  the  vessel."  Considering  what  hap- 
pened at  Ilanqiton  Roads,  more  might  liave  been  said  ;   for 


474  THE  MONITOB  TURRET.  chap,  xxxiii. 

had  the  Monitor  been  provided  with  a  wLeel-liouse  on  tlie 
top  of  the  turret,  Wordeu,  instead  of  discontinuing  the  ac- 
tion almost  blinded,  would  have  forced  the  MerrwiacJc  to 
surrender  as  readily  as  Eodgers  compelled  the  commander 
of  the  boasted  impregnable  Atlanta  to  haul  down  the  Con- 
federate flag  by  being  enabled  pei'sonally  to  direct  the  steer- 
ing and  the  firing  while  watching  from  the  elevated  turret 
wheel-house  of  the  monitor  Weehaivhen  the  movements  of 
his  opponent.  Again,  it  was  from  the  turi-et  wheel-house  of 
the  monitor  Montauh  that  the  hero  of  Hampton  Roads 
detected  the  Kasliville,  and  by  a  feAv  fifteen-inch  shells,  fired 
under  his  own  supervision,  burnt  the  Confederate  vessel  and 
cargo.  It  was  reserved  for  the  Admiral  of  the  Navy  to 
discover  that  the  arrangement  which  enables  the  commander 
of  a  mouitoi'  to  direct  the  firing  and  the  steering  from  an 
elevated  position  above  the  turret,  affording  an  all-around 
view,  is  a  great  mistake,  although  it  has  proved  so  eflicacious 
in  actual  conflict.  It  was  reserved  for  him  also  to  find  out 
"  that  the  placing  of  the  pilot-house  on  the  top  of  the  monitor 
turret  shows  a  lack  of  ingenuity " — a  discovery  apparently 
resulting  from  reflections  connected  with  the  fact  mentioned 
in  his  report,  "that  this  is  the  most  exposed  point  in  the 
vessel,  and  is  liable  to  be  swept  away  by  the  first  heavy  shot 
that  strikes."  The  Admiral  appears  to  have  forgotten  that 
the  fleet  of  monitors  at  Charleston,  commanded  by  Dahlgren, 
engaged  the  Confederate  batteries  some  twenty  times,  at 
easy  range,  and  yet  the  pilot-houses  were  not  "  swept  away." 
The  section  of   the  turret  and  wheel-house   (pilot-house) 


CHAP.  XXXIII.  THE  MONITOR  TURRET.  475 

of  a  monitor  of  the  Passaic  class  (shown  on  Plate  49)  repre- 
sents the  structure  precisely  as  built,  excepting  that  the 
turret  wall,  in  order  to  protect  the  base  of  the  wheel-house 
in  accordance  with  my  original  plan,  should  be  carried  two 
feet  above  the  turret  roof.  As  the  wheel-house  and  steering 
gear  must  remain  stationary  while  the  turret  revolves,  it 
will  be  perceived  that  tin;  plan  [iresents  a  mechanical  prob- 
lem of  no  ordinary  character.  This  is  understood  by  persons 
possessing  correct  mechanical  knowledge,  who  have  studied 
the  arrangement,  and  know  that  it  successfully  passed  the 
severe  ordeal  to  which  it  ^vas  sul)jected  during  the  war. 

With  reference  to  the  original  plan  of  extending  the 
turret  wall  above  the  roof,  it  will  be  proper  to  mention 
that  the  managers  of  the  plate-mills  employed  to  manu- 
facture the  turret  plating  during  the  war  refused  to  furnish 
plates  of  more  than  nine  feet  in  length.  Not  only  did  they 
positively  decline  to  roll  plates  of  an  additional  length  of 
six  inches,  but  they  limited  the  thickness  to  fifteen-sixteenths 
of  an  inch,  owing  to  their  inabilitj-  to  manufacture  plating 
above  a  given  weight.  Those  who  criticise  the  strength  of 
the  armor  of  the  monitors  will  do  well  to  bear  this  in  mind. 
A  careful  inspection  of  our  illustration,  representing  a  sec- 
tion of  the  turret  of  the  Passaic  class  of  monitors,  at  once 
disposes  of  the  erroneous  assertion  that  the  pilot-house,  the 
internal  diameter  of  which  is  only  six  feet,  may  be  "swept 
away."  No  target  practice  has  yet  shown  that  a  cylinder 
of  such  small  diameter,  composed  of  solid  ii'on  eighteen 
inches  thick   (of  course   it  might  be  made   thicker),  can  be 


476  THE  MOXITOB  TUHIiET.  chap,  xxxill. 

penetrated.  At  the  same  time,  the  inertia  of  such  a  cylinder, 
owing  to  its  weight,  is  so  great  that  a  base-ring  of  vei-y 
moderate  section  attached  to  the  turret  roof  will  effectually 
jii'event  dislodgment  under  the  impact  of  shot. 

In  view  of  the  foregoing,  it  "would  be  waste  of  time  to 
discuss  tlie  merits  of  the  Admiral's  I'ecommenclation  to  the 
Secretary  of  the  Navj^,  "  to  place  the  steering  apparatus 
beloAv,  with  a  small  portion  of  the  deck  above  it  raised  and 
heavily  plated,  with  apertures  to  look  through."  But  his 
reference  to  lack  of  strength  calls  for  some  notice.  In  reply, 
I  mil  simply  observe  that  by  substituting  solid  for  laminated 
armor,  the  original  If  on  if  oi;  "if  in  existence  to-day,"  would 
be  the  most  formidable  iron-clad  of  her  tonnage  possessed 
by  any  naval  power.  Of  course  it  must  be  attributed  to 
inadvertency  that  Admiral  Porter  has  not,  in  his  report, 
reminded  the  Secretary  of  the  Navy  that  the  laminated 
armor  of  the  turrets  of  the  entire  monitor  fleet  ought  to  be 
at  once  substituted  by  solid  plating. 

Naval  constractors  and  engineers  will  find  by  examining 
our  illustrations  that,  excepting  the  omission  to  place  the 
pilot-house  on  the  top  of  the  turret,  the  original  Monitor 
was  a  perfect  fighting  machine;  and  that  not  a  single  essen- 
tial improvement  has  been  added  in  building  the  subsequent 
monitor  iron-clads.  It  will  also  be  found  that  tlie  pi'opeller 
was  better  protected  in  the  original  Monitor,  and  that  the 
anchor  was  handled  with  greater  facility  and  more  perfect 
protection  to  the  crew,  tlian  in  the  recent  turret  vessels. 
Moreover,  it  is  susceptible  of  positive  demonstration  that  a 


CHAP,  xxxiii.  THE  MOMTOn   TrEJiET.  477 

vessel  built  precisely  like  the  first  Monitor,  provided  with 
a  turret  wheel-house  and  armor  of  adequate  thickness,  would 
present  the  most  perfect  vessel  for  harbor  defence  hitherto 
produced  —  whether  for  carrying  heavy  ordnance  i>r  fur 
handling  movable  torpedoes  em[)loyed  against  an  attacking 
fleet. 

It  will  be  observed  by  those  who  have  studied  the  matter 
that  Adiiiiial  Porter's  statement,  at  the  commencement  of 
his  report,  is  materially  modified  by  a  subsequent  paragi-a))h, 
strongly  recommending  the  ovcrJuing  of  the  Monitor,  "which," 
the  report  states,  "prevented  the  hull  l>eing  penetrated  if 
the  vessel  was  struck  by  a  ram."  The  Admiral  fiii-ther 
observes :  "  The  value  of  this  contrivance  was  sIkjwu  in  the 
contest  at  Hampton  Eoads,  where  the  Mrrrimacl:  rammed  the 
Monitor,  merely  turning  the  latter  half  round,  and  doing  no 
damage  whatever."  It  will  be  seen,  by  the  illustration  (PI. 
47)  representing  a  ti-ansverse  section  of  the  original  Monitor, 
that  a  collision  like  that  between  the  Iron  DuTce  and  the 
VangiiarJ,  which  sent  the  latter  to  the  l>ottom,  would  not 
be  productive  of  greater  danger  than  that  caused  by  the 
3IerrimacFs  ramming,  since,  owing  to  the  overhang  and  in- 
clined sides,  the  Ir07i  Duhe^s  spur  could  not  reach  the 
Monitor's  hull. 


CHAPTER   XXXIV. 


THE    MONITOR    ENGINE. 

(SEE    PLATES    oO    AND    51,   REPRESENTING    A   TOP    VIEW    AND    SIDE 
ELEVATION.) 


The  Engineer  of  April  20,  1866,  contains  the  following 
discussion  relating  to  tlie  engines  employed  in  the  monitor 
iron-clads,  accompanied  by  a  brief  description  of  the  me- 
chanical combination  of  these  motors : 

"The  common  feature  of  all  Ericsson's  screw-propeller 
engines,  however  otherwise  different  in  arrangement  and 
principle,  consists  in  what  he  himself  has  described  as 
'  bringing  the  power  of  two  engines  to  bear  at  right  angles 
on  a  common  crank-pin ' — a  feature  already  noticeable  in 
the  engines  built  by  him  in  1839,  at  Liverpool,  for  the 
Robert  F.  Stockton.  This  very  vessel,  tried  on  the  Thames 
so  many  years  ago,  is  stated  to  be,  even  now,  not  only  the 
most  poAverful  tug  of  her  class  on  the  river  Dela^\are,  but 
also  the  fastest.     Her  engines  consist  of  two  steam-cylinders, 


CHAP.  XX. XIV.  THE  MOKITOR  ENGINE.  479 

placeil  tliagoiially,  with  cioss-lieads  aud  side-rods  connected 
to  a  common  crank-pin  on  the  propeller-sLaft.  In  the  Edith 
and  Massachusetts  Ericsson  modified  his  diagonal  form  of 
engine  by  laying  the  cylinders  against  tiie  ship's  side,  nnder 
the  deck,  bottom  up,  with  the  piston  and  connecting-rods 
working  downwards,  but  still  connected  to  a  common  crank- 
pin  on  the  propeller-shaft.  A  couutiymaii  of  Ericsson,  Cap- 
tain Carlsund,  copied  this  arrangement,  applied  it  in  a  num- 
ber of  Swedish  vessels,  exhibited  it  at  the  Paris  Exhibition, 
and,  with  the  usual  perspicuity  of  Univei-sal  Exhibition  juries, 
was  rewarded  for  this  exhibit  by  the  great  gold  medal. 

"While  still  adhering  to  the  feature  of  bringing  the  power 
of  two  cylinders  on  to  a  common  crank-pin,  the  present  form 
of  marine  engine  adopted  by  Captain  Ericsson  may  be  looked 
upon  as  an  outgrowth  of  the  peculiar  engine,  with  semi- 
cylinders,  which  he  first  applied  to  the  United  States  steam- 
frigate  Princeton.  Excellent  illustrations  of  this  engine 
appeared  some  years  ago  in  a  work  called  'Im2)erial  Cyclo- 
paedia of  Machinery ' ;  but  as  Captain  Ericsson  has  himself 
observed,  in  a  letter  to  Mr.  Woodcroft,  the  description  began 
by  erroneously  stating  that  'Watt  has  described  a  similai" 
ari-angement  in  one  of  his  earlier  patents.'  This  is  so  far  a 
mistake,  as  AVatt — according  to  a  practice  he  adopted,  under 
the  then  state  of  the  law,  of  inserting  as  many  ideas  as 
possible  into  his  patents — merely  described  the  bare  idea 
of  a  piston  vibrating  within  a  semi-cylinder.  xVs  Captain 
Ericsson  states,  'the  Princeton^ s  engine  consists  of  compound 
or  double  semi-cylindei-  engines,  of  different  diameters,   with 


480  THE  MONITOli  EXGIKE.  chap,  xxxiv. 

pistons  attacliecl  to  tlie  common  axle  in  ojiposite  directions, 
l»otli  pistons  being  acted  upon  by  tlie  steam  at  the  same 
timt',  tlK'ir  differential  force  constituting  the  effective  motive 
power.'  The  wi'iter  of  -the  description  of  the  engines  of  the 
Princeton  in  the  '  Cyclopaedia,'  while  allowing  that  '  this 
species  of  engine  is  very  compact,'  and  that  it  '  admits  of 
being  placed  entirely  below  the  water-line,'  as  also  that, 
'  although  very  many  other  arrangements  have  been  since 
brought  out  in  this  country,  it  is  still  a  pre-eminently  suc- 
cessful engine,'  yet  observes  that  'the  friction  is,  of  course, 
more  than  in  many  others,  inasmuch  as  it  is  found  practi- 
cally impossible  to  obtain  the  power  of  steam  with  so  little 
friction  in  any  form  of  chamber  as  a  true  cylinder.'  To 
these  objections  Captain  Ericsson  replies:  'In  the  first  place, 
the  absence  of  pressure  on  the  main  journal  of  the  piston- 
shaft  is  not  understood  by  those  who  are  not  cognizant  of 
the  fact  that  a  straight  line  drawn  from  the  crank-pin  to 
the  opposite  journal  of  the  shaft  passes  through  the  centre 
of  gravity  of  the  piston.'  Then,  again,  '  the  weight  of  the 
piston,  instead  of  scraping  the  bottom  of  the  cylinder,  is 
suspended  in  the  journals,  and  there  produces  but  a  very 
small  amount  of  friction.' 

" '  Nor  have  critics  recognized  the  fact  that  during  the 
passage  of  the  crank-pin  of  the  propeller-shaft  through  the 
lower  part  of  the  arc  of  vibration,  it  is  neai'ly  relieved  from 
pressure  by  the  opposing  action  of  the  connecting-rod — one 
pushing  while  the  other  is  pulling.  Lastly,  the  absence  of 
the   great    friction  produced  by  the   diagonal    thrust   of   the 


CHAP.  XXXIV.  THU  MONITOR  ENGINE.  481 

short  coDnecting-roJ  against  the  guides  of  ordiuary  propel- 
ler engines  also  forms  an  important  item  of  saving  peculiar 
to  the  semi-cylinder  engine.' 

"  The  weak  point  in  this  very  ingenious  engine  is  un- 
doubtedly the  piston.  The  ends,  for  instance,  must  wear 
unequally  and  at  a  rate  increasing  with  the  radius  of  any 
given  point  from  the  centre  of  vibration.*  Ericsson  is  too 
good  a  mechanic  to  shut  his  eyes  to  this  fact ;  and  accord- 
ingly, when,  in  1859,  the  United  States  Navy  Department 
submitted  the  problem  of  the  best  screw-propeller  engine 
for  solution  by  the  engineers  of  America,  he  presented  a 
plan  of  an  engine  similar  to  that  of  the  Princeton  in  all 
essential  features,  with  the  exception  of  the  introduction  of 
full  cylinders  instead  of  semi-cylinders.  Since  that  pei-iod 
the  greatest  success  in  America  has  accompanied  this  last 
form  of  steam-engine ;  it  has  been  almost  universally  applied 
to  the  later  vessels  of  war  of  the  States,  and  also  in  the 
mercantile  navy  of  that  country.  There  is  not  a  single 
American  monitor  without  an  engine  of  this  kind,  and  all 
the  Swedish  monitors  are  engined  on  the  same  plan.  It 
has  been  patented  by  the  inventor,  and  the  accompanying 
plans  and  descriptions  are  prepared  from  information  sent 
by  Captain  Ericsson  himself  to  Mr.  Woodcroft  (see  Plates 
50  and  51).     He  has  also  sent  a  beautiful  model  of  it,  which 


•  In  refutation  of  this  objection,  I  have  to  state  that  the  steamship  Princeton, 
after  serving  in  tho  Golf  during  the  Mexican  War,  was  sent  to  the  JlcJiterranean 
without  repairing  her  pistons,  tho  etid-pachinga  on  examination  proving  to  be  in 
perfect  order. 


482  THE  MONITOR  ENGINE.  CHAP,  xxxiv. 

may  be  seen   in    the    Patent  Office    Museum   at  South  Ken- 
sington. 

"'The  several  direct-acting  screw-propeller  engines  hither- 
to constructed,'  says  Caj^tain  Ericsson,  '  are  all  more  or  less 
objectionable  in  the  following  particulars,  viz.  :  the  horizon- 
tal engines  occupy  too  much  space  transversely  in  the  vessel 
to  admit  of  being  placed  in  the  run ;  the  vertical  engines 
pass  through  decks,  and  project  so  far  above  the  water-line 
as  to  be  useless  for  war  purposes ;  and  all  approved  double- 
cylinder  engines  oj)erate  on  cranks  placed  at  right  angles  to 
each  other,  which  involves  a  series  of  bearings,  much  fric- 
tion, and  liability  to  derangement  from  the  shafts  getting 
out  of  line.  In  addition  to  these  imperfections,  the  extreme 
shortness  of  the  cranks,  with  the  attendant  great  friction  on 
the  crank-pins  and  journals,  to  say  nothing  of  the  heavy 
diagonal  thrust  of  the  connecting-rods,  are  serious  defects  in 
the  direct-acting  screw  propeller  engines  in  common  use.' 
In  Captain  Ericsson's  present  form  of  screw-engine  the  two 
cylinders  of  a  double  engine  are  arranged  in  such  a  manner 
that  their  base  or  bottom  ranges  with  a  plane  passing 
through  the  axis  of  the  propeller-shaft,  or  nearly  so,  in 
combination  with  a  certain  arrangement  of  rock-shafts,  crank- 
arms,  and  connecting-rods,  for  imparting  motion  from  the 
pistons  to  the  shaft,  whereby  he  is  enabled,  first,  to  bring 
the  cylinders  nearer  to  the  propeller-shaft,  and  hence  to 
economize  space  and  construct  the  frame  of  the  engine  of 
great  strength  and  compactness ;  secondlj^,  to  avoid  the 
diagonal  thrust  and  friction  of  the  slides,  unavoidable  -when 


CHAP.  XXXIV.  THE  MONITOR  EXQINE.  483 

the  connecting-rod  is  attaclied  directly  to  the  cross-bead ; 
thirdly,  to  oi)erate  the  connecting-rods  nearly  at  right  angles 
to  each  other,  ^vhich  admits  of  tlie  production  of  a  continu- 
ous motion  A\ath  a  single  ci-ank  on  the  propeller-shaft,  and 
with  a  single  crank-pin  common  to  both  engines ;  fourthly, 
to  employ  a  crank  on  the  propeller-shaft  much  longer  than 
half  the  length  of  stroke  of  the  piston,  thereby  diminishing 
the  heavy  pressure  on  crank-pins  and  on  journals,  which  has 
hitherto  caused  so  much  trouble  by  the  overheating  of  the 
bearings,  and  at  the  same  time  diminishing  the  strain  on  the 
engine-fi'ame." 

DESCRIPTIO^J"    OF    ILLUSTRATIONS    OX    PLATES    50   AND    51. 

The  general  character  of  the  Monitor  engine  will  be 
readily  comprehended  by  a  reference  to  PI.  50,  represent- 
ing a  ground-plan,  and  PI.  51,  the  side  elevation,  viewed 
from  the  bo^v  of  the  vessel.  The  crank  on  the  propeller- 
shaft  and  the  main  connecting-rods,  being  hidden  by  the 
steam-cylindei-s,  are  shown  by  dotted  lines  in  the  side  ele- 
vation. The  two  cylinders  are  placed  end  to  end  trans- 
versely in  the  vessel,  trunks  or  hollow  piston-rods  being 
cast  on  the  pistons,  as  shown  by  the  sectional  -^Iaw  on 
page  487,  projecting  outwards  towards  the  side  of  the  ves- 
sel. These  trunks  are  sufficiently  large  to  permit  the  vibra- 
tion of  links  connecting  the  pistons  and  short  vibrating 
level's  attached  to  the  for\vard  end  of  the  horizontal  rock- 
shafts.  Referring  to  the  top  view  of  the  engine,  it  Avill  be 
seen  that  vibrating  levers  of  greater  length  are  attached  to 


484  TffH  MONITOB,  ENGINE.  chap,  xxxiv. 

the  aft  end  of  tlie  rock-shafts.  These  levers  are  coupled  to 
the  common  crank-pin  on  the  propeller-shaft,  the  connecting- 
rods  acting  nearly  at  I'ight  angles  to  each  other.  By  this 
arrangement  the  throw  of  the  crank  may  be  made  much 
longer  than  in  ordinary  direct-acting  engines  ;  consequently, 
the  strain  on  the  crank-journal  of  the  propeller-shaft  will  be 
correspondingly  reduced.  A  prolongation  of  the  crank-shaft 
forward — of  small  diameter — carries  the  eccentrics  ^vhich  ac- 
tuate the  steam-valves,  while  a  prolongation  of  one  of  the 
rock-shafts  towards  the  stern  operates  an  air-pump  common 
to  both  steam-cylinders.  The  bottom  of  the  cylinders,  or 
the  division  between  them,  is  formed  as  shown  by  the  sec- 
tional plan  of  the  cylinders  before  referred  to. 

The  Chief  of  the  Bureau  of  Steam  Engineering  at  Wash- 
ington, Mr.  B.  F.  Isherwood,  having  criticised  the  principle 
of  the  Monitor  engine,  I  published  the  following  reply  in 
the  Engineer  of  June  8,  1866  : 

"  deferring  to  Mr.  Isherwood's  '  Experimental  Researches 
on  Steam-Engineering,'  I  find  it  stated,  at  page  340,  that 
the  cost  of  the  horse-power  in  the  engines  of  the  Monitor^ 
when  cutting  off  at  0.425  of  the  stroke  of  the  piston  from 
the  commencement,  is  27.7  per  cent,  more  than  in  the  U.  S. 
paddle-wheel  steamer  MicMgan.  '  Great  as  this  excess  ap- 
pears,' says  Mr.  Isherwood,  '  it  is  no  more  than  what  the 
conditions  fully  warrant  us  to  expect,  and  should  be  de- 
cisive against  the  use  of  such  a  type  of  engine.'  Mr.  Isher- 
wood accounts  for  this  great  loss  of  power  in  the  following 
manner ;    '  From   the   description   of   the  Monitor   engine,   it 


CHAP.  XXXIV.  THE  MONITOR  ENGINE.  486 

will  be  perceived  that  two  cylinders  occupy  the  same  barrel, 
the  separation  being  made  ])y  a  simple  partition  of  cast  iron 
in  the  centre.  Further,  that  during  a  large  portion  of  tlie 
time  the  boiler-steam  occupies  one  end  of  the  cylinder,  while 
the  adjacent  end  of  the  other  cylinder  is  open  to  the  con- 
denser. There  is,  consequently,  one  end  of  one  cylinder 
maintained  at  the  temperature  of  the  boiler-steam,  \vhile 
the  adjacent  end  of  the  other  cylinder,  separated  only  by  a 
cast-iron  partition,  is  exposed  to  the  temperature  of  the  con- 
denser. This  arrangement,  immaterial  as  it  appeal's — and  is 
in  a  mechanical  point  of  view — powerfully  affects  the  econ- 
omical result  by  its  great  influence  on  the  cylinder-conden- 
sation. To  appreciate  it,  it  is  only  necessary  to  imagine  the 
piston  of  the  starboard  engine,  for  example,  to  be  near  the 
outboard  end  of  its  stroke,  in  Avhich  case  nearly  the  whole 
of  the  cylinder  of  that  engine  will  be  filled  with  steam.  At 
this  moment  the  piston  of  the  port  engine  is  near  the  centre 
of  its  stroke,  and  about  one-half  of  the  port  cylinder  adja- 
cent to  the  starboard  cylinder  will  be  open  to  the  condenser 
and  exposed  to  its  refrigerating  influence;  consequently,  the 
boiler-steam  in  the  starboard  cylinder  has  been  exposed  for 
about  one-half  of  the  stroke  of  its  piston  to  this  refrige- 
rating influence  from  the  port  cylinder,  transmitted  through 
the  iron  partition  of  the  two  cylinders,  which,  as  their  dia- 
meter is  great  in  proportion  to  the  stroke  of  their  piston, 
forms  a  large  proportion  of  the  surface  in  contact  with  the 
steam.  Nor  does  the  evil  end  here ;  for,  as  the  sides  of 
both  cylinders  are  the  same  piece  of  iron — those  of  the  one 


486  THE  MONITOB  ENGINE.  chap,  xxxiv. 

being  merely  an  extension  of  tliose  of  the  other — the  con- 
duction of  heat  is  very  rapid  from  one  cylinder  to  the  other, 
and  the  heat  imparted  by  the  steam  to  the  sides  of  the 
starl)oard  cylinder  cpiickly  passes  along  by  conduction  to  the 
sides  of  the  port  cylinder,  whose  interior  is  in  communica- 
tion w'lik  the  condenser,  and  -whose  exterior  is  exposed  to 
the  atmosphere.  The  inevitable  result,  it  is  manifest,  must 
be  a  largely-increased  steam-condensation  in  cylinders  of 
this  type  of  engine  over  that  in  tlie  cylinders  of  the  usual 
type — ho^v  much  larger,  is  a  question  which  experiment  alone 
can  answer.  There  is  still  to  be  added  to  the  already-de- 
scribed peculiar  causes  of  steam-condensation  in  cylinders  of 
the  Monitor  type  of  engine  that  of  the  half-trunk,  the  effect 
of  \vhich  is,  for  a  given  capacity  of  cylinder,  to  increase 
both  the  interior  and  exterior  cylinder  surfaces  ;  while  the 
thin,  uo2>roteeted  metal  of  the  half-trunk — one  side  of  which 
is  ahvays  in  contact  with  the  atmosjihere,  while  the  other 
side  is,  too,  for  half  the  time,  and  not  only  in  contact  with, 
but  in  rapid  movement  through,  it — makes  it  a  regenerator 
of  maximum  power.' 

"  Before  analyzing  this  extraordinary  reasoning,  let  us 
examine  closely  the  section  of  the  cylinder  in  the  annexed 
diagram. 

"  It  will  be  seen  that,  although  the  two  cylinders  are 
combined  in  one  casting,  each  has  a  separate  bottom,  with 
a  considerable  space  between  the  two ;  also  that  the  heat  to 
be  transmitted  through  the  metal  of  the  cylinder,  as  Mr. 
Isherwood  states,  must  travel  a  distance  of  6  ins.  from  a  to 


CUAP.   XXXIV. 


THE  MOMTOi:  ENGINE. 


487 


b,  or  from  b  to  a,  in  less  than  half  a  second,  in  order  to 
produce  the  baneful  effect  pointed  out  by  the  author  of 
'Experimental  Researches.'  It  will  not  be  necessary  to  de- 
monstrate that  heat  cannot  be  transmitted  through  6  ins. 
of  metal  in  half  a  second,  and  it  would  be  an  insult  to  the 
intelligence  of  your  readers  to  detain  them  by  disproving 
Mr.  Isherwood's  assertion  that  a  considerable  auiouut  of  the 
motive  force  is  lost  by  thus  transmitting  heat  back  and  for- 
wards thiough  the  substance  of  the  cylinder. 


"  ^Vith  regard  to  the  supposed  rapid  transmission  of  heat 
through  the  'iron  partition  of  the  two  cylinders,'  you  will 
find  on  referring  to  the  section  that  no  transmission  of  lieat 
can  take  place,  since  the  two  Ijottoms  are  separated  by  a 
stationary  body  of  air  or  vapoi".  In  the  ordinary  cylinder- 
bottom,  the  outside  of  the  metal  acquires,  during  regular 
working  of  the  engine,  a  ]H>rmanent  temperature,  attended 
by  a  constant  loss  of  heat  radiated  into,  .ind  continually  ab- 


488  TEE  MONITOB  ENGINE.  chap,  xxxiv. 

sorbed  by,  tlie  atmosphere.  In  the  case  of  tlie  bottom-plates 
of  tlie  Monitor''s  cylinder,  a  permanent  temperature  is  also 
acquired,  but  there  is  no  loss  of  heat  by  radiation  after  the 
intervening  small  body  of  air  or  vapor  has  attained  maximum 
temperature.  It  may  be  truly  said  that  the  Monitor  engine, 
with  its  cylinders  combined  in  one  casting,  furnishes  the  only 
instance  in  which  no  heat  is  lost  by  radiation  thi'ough  the 
cylinder  bottom.  Having  thus  disposed  of  the  absurd  notion 
that  a  vast  quantity  of  heat  is  transmitted  from  cylinder  to 
cylinder,  we  now  come  to  the  question  of  increased  internal 
cylinder  sm-face  consequent  on  the  application  of  the  trunk. 
Mr.  Isherwood  ti'eats  this  question  as  one  of  such  great 
importance  that  I  have  taken  the  trouble  to  ascertain  the 
exact  amount  of  increase.  Area  of  40-inch  cylinder,  1,256 
square  inches;  area  of  IS^-inch  trunk,  143  square  inches'. 
Deducting  from  this  20  square  inches  for  a  5-in.  piston-rod, 
which  the  ordinary  engine  would  require,  we  have  a  differ- 
ence of  123  square  inches  occupied  by  the  trunk.  But  the 
trunk  only  affects  the  outboard  end  of  the  cylinder,  and 
hence  the  mean  area  taken  up  is  only  61^  square  inches. 
To  make  up  for  this  loss  of  area,  the  diameter  of  the  cylinder, 
it  will  be  found  by  calculation,  has  only  to  be  increased 
H  of  an  inch.  I  should  be  trifling  with  the  patience  of 
your  readers  were  I  to  enter  on  a  calculation  to  show  the 
amount  of  loss  attending  such  small  increase  of  the  diameter 
of  the  cylinder.  Only  one  more  point,  urged  by  Mr.  Isher- 
wood against  the  Monitor  engine  in  explanation  of  the 
asserted   27   per   cent,   loss   of  motive   force,    remains   to   be 


CUAP.  XXXIV.  THE  MONITOR  ENGINE.  489 

consideretl,  viz.,  the  effect  of  the  trunk,  which  he  calls  a 
'refrigerator  of  maximum  power.'  Mr.  Isher\vood  devotes 
so  much  time  to  the  theoretical  consideration  of  the  steam- 
engine  that  I  can  well  understand  that  he  lias  no  time  left 
for  practice;  otherwise  I  should  feel  surprised  at  his  igno- 
rance of  the  fact  that  the  great  difficulty  with  trunk  engines 
is  tliat  of  keeping  the  packing  steam-tight  without  causing 
overheating.  Experience  shows  that  the  best  that  can  be 
done  in  practice  is  to  prevent  the  trunk  fi-om  exceeding  the 
initial  temperature  of  the  steam;  and  hence  the  trunk,  in 
place  of  being  a  '  refrigerator  of  maximum  power,'  is  actually 
a  super-heater. 

"It  will  be  asked  by  what  process  did  Mr.  Isherwood 
ascertain  the  amount  of  the  assumed  loss  of  power  for  which 
he  accounts  by  this  extraordinary  reasoning?  He  placed, 
according  to  his  statement  in  'Experimental  Researches,'  a 
tank  on  a  wharf,  to  which  the  Monitor  was  made  fast.  From 
this  tank  he  supplied  the  boilers  of  the  vessel  by  means  of 
temporary  feed-pipes.  Steam  having  been  raised,  the  engines 
were  started  and  kept  in  motion  for  seventy-two  houi-s  in 
succession.  Indicator-cards  were  taken  every  hour,  by  means 
of  which  the  mean  indicated  horse-power  exerted  by  the 
engines  was  ascertained.  This  w:is  compared  witli  the  quan- 
tity of  water  measured  into  the  tank  and  supposed  to  have 
been  converted  into  steam.  The  utmost  precision  was  prac- 
tised; the  water  run  into  the  tank  was  ascertained  to  the 
tliii-(l  decimal  of  a  pound  ;  the  barometer  and  direction  of 
the  wind  carefully  noted.     The  difference  between  the  iiidi- 


490  THE  MONITOR  ENGINE.  chap,  xxxiv. 

cated  power  and  tLat  -winch  ought  to  have  been  produced 
according  to  the  quantity  of  water  used,  supposed  to  have 
been  converted  into  steam,  was  set  down  as  '  loss  occasioned 
by  cylinder-condensation.'  I  observe  that  Mr.  Isherwood's 
tables  and  calculations  make  no  allowance  for  condensation 
in  the  steam-pipes  and  valve-chests.  Loss  by  leaks  through 
the  pistons,  valves,  and  glands  ;  leaks  and  waste  of  water  and 
steam  in  the  boilers — all  these  sources  of  loss  appear  to  be 
ignored  by  the  experimentalist,  and  every  pound  of  water 
measured  into  the  tanks  is  debited  to  the  engine.  A  balance 
is  then  struck  by  deducting  the  indicated  horse-power,  and 
the  difference  put  down  as  'loss  caused  by  cylinder-conden- 
sation.' I  abstain  from  criticising  this  rough  and  unsatisfac- 
tory mode  of  deciding  the  nice  jDoint  of  cylinder-condensation  ; 
but  I  cannot  omit  adverting  to  the  fact  that,  while  the  pres- 
sui'e  in  the  boilers,  during  the  trial  of  seventy-two  hours,  was 
kept  at  17  lbs.  above  the  atmosphere,  the  pressure  admitted 
into  the  cylinders  was  only  If  lbs.  above  the  atmosphere.  The 
tables  show  that,  in  order  to  maintain  this  low  working-pres- 
sure in  the  engines,  the  throttle-valve  was  set  permanently 
at  an  opening  of  four  square  inches.  In  view  of  the  magni- 
tude of  the  engine — two  double-acting  cylinders  of  40  ins. 
diameter — the  admitting  the  steam  through  a  single  opening 
of  such  small  area  was  certainly  a  most  singular  expedient. 
Had  the  object  of  the  trial  been  to  exhibit  a  minimum  indi- 
cated horse-power,  a  more  effective  expedient  could  not  have 
been  devised.  As  the  mean  area  of  the  piston,  according  to 
the   tables,   was    1,185   square   inches— about    three   hundred 


CHAP.  XXXIV.  THE  MOXTTOR  EXOINE.  491 

times  greater  than  the  area  of  the  throttle-valve — the  speed 
of  the  pistons  being  at  the  same  time  upwards  of  2.5  feet 
pt'i-  second,  some  idea  may  be  formed  of  the  amount  of  dy- 
namic force  exerted  and  heat  extinguished  in  passing  the 
steam  from  the  boilers  to  the  engines.  Yet  this  waste  of 
force  was  ignored  by  the  experimentalist,  and  the  indicated 
piston-power  alone  was  set  against  the  water  measured  into 
the  tank. 

"  Apai't  from  these  facts,  the  most  critical  examination 
of  the  sectional  plan  of  the  cylinders  of  the  Monitor  before 
refei'red  to  (see  page  487)  fails  to  discover  any  error  of  con- 
struction productive  of  cylinder-condensation  to  a  greater 
extent  than  in  the  screw-engines  of  the  most  celebrated 
makers." 


CHAPTER   XXXV. 

THE   MONITOR   DICTATOR. 

(SEE   PLATES    52,    53,    54,    AND    55.) 


The  Dictatoi'  is  the  most  powerful  and  efficient  fighting- 
ship  possessed  by  the  United  States.  Like  the  Monadnock 
class  of  monitors,  she  is  also  a  good  cruising  vessel.  The 
hull,  engines,  turret,  and  gun-carriages  of  this  ship  were  de- 
signed and  furnished  by  the  writer,  under  a  contract  with 
the  United  States  Navy  Department,  1862.  Her  length  on 
deck  is  314  ft.,  the  overhang  aft  being  31  ft.,  and  the  for- 
ward overhang  13  ft.,  leaving  a  length  of  270  ft.  between 
perpendiculars  (see  side  elevation,  PI.  52).  Her  breadth 
over  the  sides  is  41  ft.  8  ins.,  and  her  total  beam  50  ft., 
whilst  her  draught  is  20  ft.,  the  sides  midships  projecting 
only  1  ft.  G  ins.  above  the  water-line.  The  sides  are  pro- 
tected at  and  near  the  water-line  by  11  ins.  of  wrought  iron, 
this  thickness  consisting  of  inner  bars  5  ins.  thick,  and  six 
plates  each  1  in.  thick  (see  transverse  section,  PI.  58).  The 
plates    are    placed    upon  massive    timber  backing,   as    shown 


CHAP.  XXXV.  THE  MOXITOIi  DICTATOR.  493 

by  the  illustration  on  the   plate   referred   to.      Her   tonnage 
is  3,000  tons. 

The  engines  of  the  Dictator  (see  illustrations  on  Plates 
53  and  54)  are  4,500  indicated  horse-power,  consisting  of  a 
pair  of  vertical  cylinders  100  ins.  in  diameter,  with  a  stroke 
of  4  ft.  The  pistons  have  small  trunks  on  their  upper 
side,  and  are  connected  by  links  with  the  ends  of  curved 
horizontal  amis  attached  to  the  forward  end  of  rock- 
shafts  placed  outside  the  cylinders  slightly  above  the  latter. 
Straight  arms  nearly  vertical  are  attached  to  the  after-ends 
of  the  rock-shafts.  These  arms  are  coupled  by  means  of 
diagonal  connecting-rods  to  a  common  crank-pin  fixed  near 
the  circumference  of  a  fly-wheel  upon  the  screw-shaft.  The 
engines  drive  a  propeller  21  ft.  G  ins.  in  diameter,  provided 
with  four  blades  set  at  a  pitch  of  34  ft.  The  propeller 
weighs  39,000  lbs.,  and  its  shaft  36  tons.  The  engines  are 
supplied  with  steam  by  six  boilers  having  altogether  50 
furnaces;  the  total  grate-surface  is  1,128  square  feet,  and 
the  heating  surface  over  32,000  square  feet.  The  coal-bunkers 
accommodate  600  tons  of  coal. 

The  Dictator  has  a  single  revolving  turret,  essentially  the 
same  as  that  delineated  on  Plate  49;  it  is  24  ft.  in  diameter 
inside,  by  9  ft.  high,  and  contains  two  fifteen-inch  guns. 
The  sides  of  the  turret  are  built  up  of  two  separate  concen- 
tric cylindei-s,  composed  of  plates  1  inch  thick  firmly  riveted 
together,  a  space  of  five  inches  being  formed  between  the 
said  cylinders.  This  space  is  filled  with  segmental  wi-ought- 
iron  slabs   5   ins.    thick    and    12    ins.    broad;  hence  the  total 


494  THE  MONTTOR  DICTATOB.  CHAP.  XXXT. 

thickness  of  tlie  turret  wall  is  1  ft.  ?>  ins.  The  turret  has  a 
bell-mouthed  top  formed  of  iron  plates  i  in.  thick,  curved 
outwards,  as  shown  on  Plate  52,  for  the  pui-pose  of  throw- 
ing oft'  the  water  which,  during  heavy  weather,  is  dashed 
up  the  sides  of  the  turret.  Around  the  bell-mouthed  top 
mentioned  is  carried  a  wooden  grating  provided  with  a 
hand-rail,  and  appropriate  stanchions  for  supporting  an  awn- 
ing. The  grating  referred  to  forms  a  convenient  balcony 
for  promenade.  Over  the  centre  of  the  turret  is  placeil  the 
pilot-house,  which  is  8  ft.  in  diameter  in  the  inside,  and 
7  ft.  high,  its  sides  being  formed  of  twelve  thicknesses  of 
1-in.  plates.  This  structure  is  supported  by  a  strong  cross-' 
beam  which  rests  upon  a  collar  formed  on  a  strong  central 
■\vrouglit-iron  shaft  passing  down  through  the  turret ;  this 
shaft  being  stationary,  the  turret  revolving  round  it.  Except- 
ing the  bell-mouthed  plate-iron  extension  at  the  top,  the 
Dictator  turret  is  constructed  precisely  as  the  turrets  of  the 
Passaic  class  of  monitors  delineated  ou  Plate  49.  Referring 
to  this  delineation,  it  will  be  seen  that  the  weight  of  the 
turret  wall  is  suspended  by  diagonal  rods  in  such  a  manner 
that  the  entire  weight  of  the  turret  and  armament,  as  well 
as  the  pilot-house,  is  sustained  by  the  stationary  central  shaft. 
The  latter  rests  on  a  casting  bolted  to  the  transverse  bulk- 
heads of  the  ship,  as  shown  in  Plate  4:7.  The  pilot-house 
is  provided  with  sight-holes  placed  at  a  convenient  height, 
and,  like  the  centi;al  shaft,  is  stationary.  The  diagonal  rods 
before  referred  to,  it  should  be  observed,,  are  furnished  with 
screw-euds  and  nuts,  in  order  to  admit  of  their  being  tightened 


CUAP.  xxxv.  TJIE  MOMTOJi  DICTATOB.  495 

in  case  the  turret  wall  sliuuld  sjig.  The  cross-beam  before 
mentioned,  which  extends  across  the  top  of  the  turret,  sup- 
l)ort8  rafters  carrying  iron  bars  4  ins.  deep  by  3  ins.  wide, 
and  2^  ins.  apart,  these  bars  being  covered  with  peii'oiatetl 
plates  1  iu.  thick.  The  base  of  the  turret  wall  rests  on  a 
flat  ring  composed  of  bronze,  the  under-side  of  which  is  accu- 
rately faced.  It  is  supported  by  anotliei-  Hat  ring  faced  on 
the  top  and  secured  to  the  deck.  By  this  means  a  water- 
tight joint  is  formed  between  the  base  of  the  turret  wall 
and  the  deck.  It  is  obvious  that  considerable  power  would 
be  required  to  cause  the  turret  to  revolve  if  its  weight 
rested  on  the  I'iugs  described.  Accordingly,  a  taper  key 
is  inserted  under  the  stationary  central  shaft,  by  which  the 
weight  of  the  turret  and  appendages  may  be  raised  so  as 
to  rest  wholly  on  the  shaft.  During  the  war  this  key  was 
invariably  tightened  before  going  into  action,  hence  the  tur- 
rets revolved  with  perfect  freedom  while  the  gunners  pointed 
the  pieces.  A  circular  cliunuel  is  formed  iu  the  deck  near 
the  inside  of  the  turret,  in  order  to  carry  off  water  that  may 
leak  under  the  base.  It  is  conducted  to  the  bilge  by  small 
scuiiper-pipes.  The  machinery  for  turning  the  turret  con- 
sists of  a  pair  of  donkey-engines,  which  work  gearing  con- 
nected with  a  large  cog-wheel  secured  by  strong  lugs  to 
the  under-side  of  the  gun-slides,  which  are  in  their  turn 
tirmly  attached  to  the  sides  of  the  turret.  It  should  be 
observed  that  all  the  turning  gear  is  below  the  deck-line. 
The  floor  of  the  pilot-house  consists  of  a  wooden  grating 
fitted  with  hinged   hatches,   through   which  the  captain  and 


496  THE  MONITOR  DICTATOR.  chap.  xxxv. 

steersman  enter  from  tlie  turret.  The  steering-wheel  is  con- 
tained in  the  pilot-house,  and  its  motion  is  transferred,  by 
gearing  and  by  a  rack  sliding  in  a  groove  formed  in  the 
central  shaft,  to  a  pinion  fixed  upon  the  axle  of  the  steering 
barrel  belo^v.  From  this  barrel  chains  extend  to  the  rudder, 
which  is  of  the  balanced  kind.  The  vessel  is  strengthened 
beneath  the  turret  by  transverse  and  longitudinal  bulkheads. 

The  gun-carriages  are  run  out  upon  their  slides  by  means 
of  winch-handles  moving  wheel-work  geared  into  racks,  the 
friction-gear  being  tightened  as  soon  as  the  pieces  are  full 
out,  and  of  course  relieved  immediately  after  the  recoil.  Each 
gun  has  a  radial  bar  placed  above  it,  upon  which  runs  a  wheel 
supporting  a  block  and  tackle,  provided  with  a  small  dished 
platform  upon  which  the  shot  is  placed.  By  this  contrivance 
the  shot  can  be  rapidly  raised  from  the  shot-locker  to  the 
muzzle  of  the  gun. 

In  the  Dictator  the  air  required  for  ventilation  and  for 
supplying  the  boiler-furnaces  is  drawn  in  by  several  large 
fan-blowers,  partly  through  the  top  of  the  turret  and  partly 
thr(.)ugh  shot-proof  trunks  carried  high  above  the  decks,  as 
shown  in  the  side-elevation,  Plate  52.  The  vessel  is  provided 
with  a  spacious  platform  or  promenade  deck,  placed  at  nearly 
the  same  height  as  the  top  of  the  turret  (see  plate  referred 
to).  This  deck  is  supported  on  vertical  iron  stanchions,  the 
ship's  boats  being  suspended  below  the  same.  The  cabins 
are  lighted  by  means  of  bull's-eyes  fitted  into  brass  frames 
let  into  the  deck,  .these  frames  being  replaced  by  solid 
wrought-ii'on  covers  when  the  ship  is  going  into  action. 


CHAP.  XXXV.  T£I£  MONITOR  DICTATOE.  497 

The  Engineer,  in  au  article  published  1866,  states  with 
reference  to  the  Dictator : 

"  It  may  be  laid  down  as  a  general  axiom  that  when  the 
introduction  of  fresh  elements  into  any  mechanical  problem 
has  effected  a  revolution  in  its  first  conditions,  originality  is 
at  great  advantage  over  hesitating  and  long-pondering  judg- 
ment. Though  without  the  advantages  which  our  great 
command  over  iron  in  large  masses  has  given  in  the  modern 
substitution  of  iron  for  wood  in  naval  warfare,  the  Ameri- 
cans have  certainly  shown  much  originality  and  boldness  in 
their  designs  for  war-shi^js.  A  good  deal  of  this  is  due  to 
Captain  Ericsson — an  original  thinker  and  constructor,  \vhose 
very  originality  would  have  led  him  to  be  distrusted  in 
this  conservative  countiy.  Broadly  stating  the  matter,  it 
may  be  said  that  in  France  and  in  England  we  have  pretty 
much  confined  ourselves  to  bolting  massive  iron  slabs,  with 
an  intermediate  packing,  to  the  skins  of  our  iron  vessels  of 
war ;  but  Ericsson  has  taken  a  much  more  comprehensive 
view  of  the  capabilities  of  engineering  in  its  application  to 
the  eternal  war-problem  of  doing  as  much  damage  as  pos- 
sible to  your  adversary  with  as  little  as  possible  harm  to 
yourself." 


CHAPTER  XXXVI. 

THE   MONITOR  TURRET  AND   THE  CASEMATE. 
(SEE   PLATE   56.) 


An  opportunity  of  instituting  a  direct  comparison  between 
the  monitor  turret  and  the  fixed  casemate  was  furnished 
by  the  completion  of  the  Turkish  armor-chxd  vessel  Moijini 
Zaffer,  launched  on  the  Thames  in  June,  1869.  The  build- 
ing and  arming  of  this  iron-clad  being  the  result  of  the 
Joint  efforts  of  Sir  William  Armstrong,  Samuda,  and  Raven- 
hill,  we  have  a  guarantee  that  whatever  merits  the  fixed 
casemate  system  possesses  have  been  fairly  developed  in  this 
attemj)t  to  supersede  the  monitor. 

It  cannot  fail  to  be  noticed,  on  careful  examination  of 
the  illustrations  on  the  plate  referred  to,  that  the  planning 
of  the  casemate  of  the  Moyini  Zaffer  shows  much  thought 
and  elaboration ;  also  that  the  complication  whicli  character- 
izes its  form  is  evidence  that  the  planner  was  dealing  with 
a   difficult  subject.     Nor   can  the  attentive   observer  fail  to 

498 


CUAP.  XXXVI.     THE  MOSITOE  TURUET  AND  TUE  CASEMATE.      499 

see  at  a  glauce  how  imperfectly  the  dij^aJvantages  atteutling 
the  elougatiuu  and  immobility  of  the  battery — viz.,  the  limited 
horizontal  range  of  the  guns — have  been  overcome  by  the 
combination  of  curvature  and  angles  resorted  to  by  the  con- 
structor of  this  substitute  for  the  monitor  turret. 

Our  illustrations,  besides  representing  a  top  view  of  the 
Moyini  Zaffer,  accurately  drawn  to  scale,  also  represent  a  top 
view  of  a  monitor  provided  with  two  turrets  of  the  same 
diameter  as  those  of  the  Pasmic  cLiss — viz.,  21  feet  internally. 
The  length  of  the  Turkish  vessel  is  230  feet,  with  35  feet 
G  inches  beam.  The  monitor,  for  the  sake  of  exact  com- 
parison, has  the  same  dimensions ;  but  the  thickness  of  its 
armor  is  greater  than  that  of  the  former,  and  so  proportioned 
that  the  %oeujlit  of  armor  of  both  vessels  is  alike.  The  free- 
board of  the  Moyini  Zaffer,  as  in  all  iron-clads  built  by 
English  engineei-s,  is  several  times  higher  than  that  of  the 
monitor,  and  consequently  deeper  armor  below  water  must 
be  applied  to  afford  protection,  increased  rolling  being  the 
inevitable  result  of  high  freeboard.  Referring  to  the  bat- 
teries, it  ^^^ll  be  seen  that  the  circumference  of  the  fixed 
liattery  is  greater  than  that  of  the  two  turrets  in  the  ratio 
of  25  to  15. 

The  Engli-sh  mechanical  journals,  in  describing  the  Moyini 
Zdffii;  point  with  apjiarent  satisfaction  to  the  circumstance 
that  this  casemate  ship,  which  is  intended  for  the  defence 
of  the  Bosporus,  has  armor-plates  "generally  six  inches  in 
thickness,  the  whole  of  the  battery  (backed  with  wood) 
being  cased  with  5-inch  plates."     The  battery,  though  pierced 


500      THE  MONITOB  TUFRET  AND  THE  CASEMATE,    chap,  xxxvi. 

for  eight  guns,  will  only  carry  four  of  Armstrong's  12-ton 
riiles.  Tlie  intention  being  to  transfer  the  pieces  from  one 
side  of  tlie  battery  to  the  other  during  action,  it  is  evident 
that  Sir  William  has  reached  the  limit  of  weight.  The 
difficulty  of  changing  sides  with  the  rapidity  called  for  dur- 
ing contest  with  screw-propelled  assailants  needs  no  explana- 
tion. But  the  constructor  of  the  monitor  turret,  which,  as 
our  illustration  shows,  commands  340  deg.  of  the  horizon,  is 
not  hampered  by  considerations  of  weight  of  metal,  a  24-ton 
gun,  or  even  one  weighing  forty-eight  tons,  being  pointed  as 
readilj^  by  turning  the  turret  as  the  lightest  field-piece. 
Accordingly,  the  monitor  which  our  illustration  represents 
is  mounted  with  four  24-ton  guns. 

Making  proper  allowance  for  the  greater  area  of  side- 
armor  and  battery-plating  of  the  Moyini  Zaffer,  it  will  be 
found  that  our  double-turreted  monitor  will,  on  the  same 
draught  of  water,  support  10-inch  thick  side-armor,  15-inch 
thick  turret-plating,  and  carry  four  24-ton  guns.  The  greater 
security — we  might  say  the  impregnability — thus  attained 
by  the  monitor  form  is,  however,  only  a  part  of  the  ad^'antage 
of  this  system  over  that  which  is  represented  by  the  Turkish 
iron-clad — the  latest  endeavor  of  some  naval  constrictors  to 
demonstrate  that  the  conflict  at  Hampton  Roads  was  not, 
after  all,  so  decisive  as  supposed. 

Impregnability  and  calibre,  although  very  important,  by 
no  means  decide  the  superiority  of  armored  vessels ;  hori- 
zontal range  is  in  many  cases  of  equal  importance.  A  monitor 
hull  provided  with  a  fixed  battery  may  be  made  as  impreg- 


CHAP,  xxxvr.     THE  MOXITOn  TUFnET  AND  THE  CASEMATE.      501 

nable  as  a  complete  monitor,  but  at  least  two-tliii-ds  of  the 
guns  of  such  a  vessel  will  be  ineffective  in  battle.  Samuda, 
evi(lentl)',  was  fully  aware  of  tlie  impotency  of  his  artilleiy, 
owing  to  limited  horizontal  iviiige,  when  he  adopted  the 
complicated  form  of  the  battery  of  the  Moijini  Zaffer. 

Let  us  now  consider  in  detail  this  question  of  horizontal 
range,  and  inspect  closely  the  extent  of  ranges  marked  on 
oiii'  illiistraticin  foi'  each  gun  separately.  The  ranges  olitained 
by  the  fixed  battery  of  Samuda's  construction  first  claim 
our  attention.  To  avoid  confusion,  the  ports  have  been  let- 
tei'ed  a,  />,  c,  and  '/,  the  first  letter  denoting  the  forward  poi't 
of  the  battery,  and  also  the  muzzle  of  the  piece  belonging 
thereto.  Beginning  with  the  first-mentioned  port,  it  will  be 
seen  that  each  gun  respectively  ranges  over  a  field  of  96,  98, 
98,  and  02  deg.  Referring  to  the  monitor,  it  will  be  seen 
that  each  of  the  four  guns  sweeps  a  field  of  170  deg.  It 
should  be  observed  that  the  ranges  marked  on  the  illustra- 
tion have  reference  only  to  the  starboard  side  of  the  line  of 
keel. 

It  will  be  proper,  before  assigning  a  numerical  value  to 
the  eflSciency  of  each  of  the  systems  under  consideration,  to 
remember  that  the  real  power  of  naval  artilleiy  is  determined 
by  niiiUiplying  the  weight  of  shot  by  "the  horizontal  ranfife, 
the  position  of  the  vessel  remaining  constant.  ^Modern  taro^et 
practice  having  demonstrated  that  a  24-ton  gun  is  capable 
of  throwing  a  projectile  o"f  600  pounds  with  adequate  force, 
and  that  a  12-ton  gun  is  about  the  projier  size  for  .'JOO-jKmnd 
projectiles,  we  are  enabled,  by  applying  the  rule  befoi-e  men- 


502     THE  MOKITOE  TUBBET  AND  THE  CASEMATE,      chap,  xxxvi. 

tioned,  to  determine  with  exactness  the  rehative  efficiency  of 
the  monitor  turret  and  the  fixed  battery  or  casemate.  The 
power  of  the  forward  gun  a  of  the  casemate  will  accordingly 
])e  represented  by  300  X  96  =  28,800.  In  like  manner,  by 
multiplying  the  -weight  of  the  projectiles  of  the  remaiuino- 
three  guns  by  their  respective  ranges  in  degrees,  we  obtain 
a  sum  total  of  115,200.  Applying  the  same  mode  of  com- 
putation to  the  monitor — viz.,  multiplying  600  X  170  X  4 — 
we  establish  the  important  fact  that  the  actual  efficiency  of 
the  monitor  is  to  that  of  the  casemate  vessel  as  408  to  115, 
Apart  from  this  superiority  as  regards  the  artillery  of  the 
monitor  over  that  of  the  Turkish  iron-clad,  the  armor  of 
both  battery  and  hull  of  the  latter  is  wholly  insufficient  to 
compete  with  the  former.  The  inference,  therefore,  is  obvious 
and  irresistible  that  the  monitor  represented  by  our  illus- 
ti'ation  could  readily  destroy  Samuda's  casemate  vessel.  But 
it  is  not  my  intention  to  prove  the  worthlessness  of  the 
Moyini  Zaffer  as  a  war  vessel,  the  object  of  discussing  the 
subject  being  simply  that  of  instituting  a  comparison  between 
the  two  systems  represented  by  the  illustrations  on  Plate  5G. 
It  merits  special  attention  that,  apart  from  the  limited 
horizontal  range  of  all  the  guns  of  the  Moyini  Zaffe>\  only 
one  of  the  four — viz.,  a — can  be  j^ointed  forward  parallel  w^ith 
the  ship's  course;  and  that  c,  the  only  other  gun  capable  of 
firing  ahead,  cannot  point  nearer  than  11  deg.  of  the  line  of 
keel.  At  a  distance  of  a  mile  ahead,  there  is,  consequently, 
a  field  of  1,200  feet  which  an  assailant  may  occupy,  ex2:)osed 
to  only  one  12-ton  gun.     Chased  by  an  enemy,  the  Turkish 


CUA1-.  xxxvi.     lUE  MoyiTOU  TLliliET  AM)  TUE  CASEMATE.      5013 

\var-shii),  with  the  Saimuhi-Aiiiiiitioug  battery,  will  be  eiiually 
impotent;  the  gun  marked  d  being  her  only  defensive  wea- 
l)on.  It  will  be  founil,  on  inspection,  that  the  piece  marked 
b,  like  that  marked  c,  cannot  be  pointed  nearer  than  1 1  de"'. 
of  the  line  of  keel. 

Let  us  now  turn  to  the  monitor.  It  will  be  seen  that 
four  24-ton  guns,  two  forward  and  two  aft,  fire  in  a  direct  line 
with  the  keel;  there  being  no  safe  position,  as  in  the  case 
of  the  fixed  battery,  for  the  enemy's  vessel  to  occupy.  The 
entire  field,  viewed  from  stem  to  stern,  as  the  plan  shows, 
is  swept  by  all  the  guns  of  the  monitor.  Bearing  in  mind 
that  these  powerful  guns  are  protected  by  15-iuch  thickness 
of  iron,  which,  if  applied  in  two  thicknesses,  is  proof  against 
any  artillery  yet  produced,  wliile  the  1 2-ton  guns  of  the 
Samuda-Armstrong  battery  are  protected  by  armor  which  a 
7-inch  rifle  will  pierce  through  and  through,  the  argument 
in  favor  of  the  monitor  turi-et  becomes  overwhelming. 

It  will  be  asked,  in  view  of  these  incontrovertible  facts, 
why  do  constructors  advocate  the  fixed  battery?  I  know  of 
no  other  reason  than  the  assumption  that  the  joint  between 
the  rotating  turret  and  the  deck  cannot  be  made  secure. 
English  engineers,  relying  on  the  accounts  of  the  perform- 
ances of  the  monitors  published  by  the  enemies  of  the  Union 
during  the  war,  apparently  do  not  take  the  trouble  to  investi- 
gate the  matter;  while  American  experts  who  have  written 
about  turrets  appear  to  be  ignorant  of  the  leading  facts 
connected  with  the  turret  system. 

For  instance,  Mr.  Eads,   in  a  report  to  the  Navy  Depart- 


504      THE  MOXlTOli  TUltBET  AND  THE  CASEMATE,    chap,  xxxvi. 

meut,  informs  the  Secretary  that  "  the  baud  rouud  the  base 
of  the  tui-ret  on  the  Dictator  weighs  over  20,000  pounds," 
aud  points  out  how  much  better  this  great  weight  of  irou 
might  be  applied  for  other  purposes.  Now,  this  turret  has 
no  baud  rouud  its  base,  nor  was  it  ever  intended  to  have 
one,  Mr.  E.  also  tells  the  Secretary  that  auy  down^vard 
swelling  of  the  plating,  produced  by  the  impact  of  projec- 
tiles striking  low,  will  stop  the  rotation  of  the  turret  by 
friction  under  its  base.  This  assertion  proves  ignorance  of 
the  fact  that  the  Diotatoi'  turret  rests  wholly  on  the  four 
inner  courses  of  plating  (which  cannot  be  swelled),  and  that 
the  intermediate  wrought  slabs  and  outer  plating  (together 
11  inches  in  thickness)  do  not  reach  the  deck.,  aud  therefore 
can,  by  no  possibility,  cause  the  predicted  stoppage.  Again, 
the  apprehensions  expressed  in  several  reports,  with  reference 
to  the  base  of  the  pilot-house  in  connection  with  the  rotation 
of  the  turret,  prove  that  another  very  important  circumstance 
has  been  overlooked — viz.,  that  the  turret  projects  consider- 
ably above  said  base,  thereby  effectually  protecting  it. 


CHAPTER  XXXYII. 

CARRIAGES  FOR  HEAVY  ORDNANCE. 
(SEE   PLATE   57.) 


The  Engineer,  in  discussing  the  subject  of  gun-carriao'es 
(in  1868),  says:  "Americans  mount  their  big  guns  in  turrets, 
and  France  has  no  peculiarly  big  guns  to  mount.  In  the 
matter  of  carriages,  as  in  almost  everything  else  connected 
with  recent  improvements  in  ordnance,  England  must  be 
content  to  act  as  schoolmistress  to  the  rest  of  the  world." 
This  assertion  is  preposterous,  in  view  of  the  fact  that  Eng- 
land had  not  mounted  a  single  heavy  gun  on  shipboard  at 
the  time  when  we  had  a  large  fleet  of  iron-clad.s  armed  with 
11  and  15  inch  guns.  Not  only  that:  we  iiad  effectually 
used  those  guns  in  numerous  engagements,  and  fully  estab- 
lished the  reliable  character  of  our  system  of  mounting  the 
same,  before  English  artillerists  believed  it  possible  to  dis- 
pense with  breeching.  But  our  contest  was  watched  by 
attentive   eyes,  and   hence   our   success  did  not  long  remain 


506  OABBIAOES  FOB  HEAVY  OBDNANOE.         chap,  xxxvii. 

a  secret.  An  enterprising  English  captain  sjjeedily  pro- 
cured drawings  of  tlie  Monitor  gun-carriages  and  tlieir  fric- 
tion-gear. Ho^v  faitlifully  lie  copied  our  system  the  reader 
will  see  by  comjjaring  tlie  several  devices  for  producing 
friction  represented  on  Plate  57.  Sir  William  Armstrong, 
too,  becoming  convinced  that  the  Monitor  friction-gear  was 
the  best  for  checking  the  recoil  of  naval  ordnance  of  heavy 
calibre,  also  follo\ved  our  lead.  An  anuising  contest  arose 
between  Sir  AVilliam  and  the  enter2:)rising  naval  officer  al- 
luded to,  whose  indignation  knew  uo  bounds  on  finding 
that  the  great  gunmaker  had  adopted  the  same  plan  as  him- 
self for  checking  the  recoil.  But  Mr.  Scott  Russell  having 
in  the  meantime  published  accurate  drawings  of  the  Monitor 
gun-carriages  and  friction-gear.  Sir  William  was  in  a  posi- 
tion to  silence  the  complaints  of  his  rival  by  simply  point- 
ing to  Plate  No.  139  of  Scott  Eussell's  great  work  on  naval 
architecture. 

By  referring  to  the  illustration  mentioned,  the  reader 
will  see  at  a  glance  that  Captain  Scott's  friction-gear  is  iden- 
tical with  that  applied  to  the  gun-carriages  of  the  American 
iron-clad  fleet.  The  principle  is  very  peculiar,  and  involves 
the  apparent  paradox  of  obtaining  increased  friction  to  any 
desirable  extent  without  adding  to  the  force  employed.  A 
brief  explanation  will  show  how  this  singular  result  is  ef- 
fected. A  series  of  vertical  plates  are  secured  to  the  lower 
part  of  the  gun-carriage  in  such  a  manner  as  to  admit  of  a 
slight  transverse  movement.  These  plates  slide  freely  be- 
tween   longitudinal    friction-timbers,    or   })lanks    composed  of 


CHAP.  XXXVII.         CAIil'IAGLS  I'OI!  HEAVY  OEDyAXCK  607 

hard  wood,  which  in  broadside  vessels  are  attached  to  tlie 
"slides,"  and  in  the  monitoi-s  secured  to  the  base  of  the 
turrets.  It  will  he  readily  understood  that,  l)y  applying 
lateral  force  to  the  two  outside  vertical  plates  from  \\itli- 
out,  friction  will  be  established  between  all  the  plates  and 
the  intervening  planks ;  and  it  will  be  evident  that  the 
amount  of  friction  between  the  surfaces  in  contact  will  de- 
pend on  the  force  thus  applied,  wholly  independent  of  their 
7iumhei:  Thus,  by  merely  doubling  the  number  of  plates 
and  idanks,  the  friction  will  be  doubled  without  callino'  for 
the  application  of  any  additional  force.  It  rarely  hajipens 
in  mechanical  contrivances  that  the  effect  to  be  produced  is 
so  completely  independent  of  the  force  applied  as  in  this 
instance.  The  practical  advantage  of  obtaining  requisite 
friction  without  employing  great  manual  power  is  obvious  ; 
and  that  it  is  fully  appreciated  may  be  infeired  from  the 
alacrity  with  which  the  system  has  been  copied  in  Euroj^e. 
The  difficulty  of  handling  the  modem  monster  guns  on 
board  ship  in  l)ad  weather,  ^vllich  at  one  time  was  deemed 
impracticable  by  experienced  sailors,  vanished  with  the  in- 
ti'oduction  of  my  multiple.x  friction  apparatus  thus  briefly 
described.  The  reader  will  observe  how  closely  even  the 
detail  of  the  original  has  been  followed  by  the  plagiarists  ; 
the  mode  of  pi'oducing  the  lateral  pressure,  for  instance,  has 
been  carefully  copied  by  Captain  Scott.  lie  employs  the 
transvei-se  screw  and  vertical  levers  by  which  the  outside 
friction-plates  are  forced  inwards,  precisely  as  in  the  Monitor 
carriages.      Sir   William    Armstrong  also  emplojs  the   trans- 


508  GAliBIAGES  FOB  HEAVY  OBDNANGE.       chap,  xxxvii. 

verse  screw  and  vertical  levers,  but  lie  divides  the  screw  in 
the  middle — an  ill-considered  modification,  as  it  calls  for  the 
application  of  force  on  both  sides  of  the  carriage,  increases 
tlie  friction,  and  tends  to  pull  the  sides  together.  Sir  Wil- 
liam Armstrong  also  introduces  the  modification  of  employ- 
ing iron  bars  in  place  of  the  wooden  friction-planks — a  most 
objectionable  expedient,  as  the  needed  friction  is  greatly 
diminished  by  presenting  metal  against  metal.  Moreover, 
the  friction  becomes  so  irregular  as  to  bafHe  any  attempt  at 
systematic  tightening  with  reference  to  the  charge  of  pow- 
der employed,  rendering  accidents  inevitable.  It  is  evident 
that  if  the  metallic  plates  are  kept  dr}",  abrasion  follows,  and 
that  their  surfaces  are  liable  to  cut  and  stick.  If  oiled,  the 
least  excess  of  lubrication  will  reduce  the  friction  to  such 
an  extent  as  to  permit  the  gun  to  recoil  without  check,  as 
experience  during  experimental  practice  has  shown.  Apai't 
from  these  objections,  the  want  of  that  indispensable  elas- 
ticity which  the  wooden  friction-plank  affords  is  fatal  to  Sir 
William  Armstrong's  substitution  6f  metal  for  wood. 

With  such  facts  before  it,  the  Engineer  tells  its  readers 
that,  in  the  matter  of  carriages  and  other  improvements 
connected  with  naval  ordnance,  England  must  be  content  to 
act  as  "  schoolmistress  "  to  the  rest  of  the  world. 

Alas  for  the  schoolmistress  !  She  has  been  endeavoring 
to  teach  the  \vorld  for  a  long  time  that  our  system  of  naval 
defence  was  all  wrong,  until  at  last  she  has  discovered  that 
her  boasted  broadside  iron-clads,  on  which  millions  have 
been  spent,  are  hopelessly  \nilnerable. 


CHAP.  XXXTII.         CAEFTAGES  FCW   ]TEArT  ORDNAKCK  509 

The  leading  journal  of  England,  Februaiy  12,  1SG8,  frankly 
admits  that  "the  final  blow"  has  been  given  to  the  "already 
tottering  theory  of  broadside  iron-clads,"  and  adds:  "Why 
do  we  obstinately  refuse  to  build  small  iron-clad,  sino-le- 
tuiret  vessels,  with  low  freeboard,  and  one  or  two  guns  of 
the  heaviest  calibre?  The  American  and  Russian  officei-s 
who  have  actually  tried  them  report  with  enthusiasm  of 
their  sea-going  properties."  It  would  have  been  well  for  the 
"schoolmistress"  if  she  had  not  listened  to  the  advice  which 
prejudiced  naval  constructors  have  persistently  tendered  ;  it 
might  have  spai-ed  the  naval  administration  of  England  the 
severe  censure  called  forth  at  the  time  for  having  neglected 
to  adopt  the  monitor  system.  "  It  seems  to  us,"  says  the 
Times  of  the  date  before  mentioned,  "  that  the  Admiralty 
have  in  nothing  so  neglected  their  duty  as  in  failing  to 
provide  us  with  a  large  supply  of  these  formidable  little 
vessels." 

Can  the  Enghieei\  moreover,  point  to  a  single  invention 
connected  with  our  turret  iron-clads,  naval  ordnance,  or  gun- 
carriages  which  has  originated  in  England  ?  Those  best 
acqutiinted  with  the  matter  know  that  every  mechanical  de- 
vice relating  to  the  system  Avhich  so  successfully  vindicated 
itself  dui-ing  the  late  wai-  was  contrived  on  this  side  of  the 
Atlantic — a  success  the  more  remarkable  since  the  exigency 
of  the  time  did  not  admit  of  previous  expeiinients,  everv- 
thing  being  despatched  directly  from  the  foundr}-  and  woi-k- 
shop  to  the  scene  of  conflict. 


CHAPTER   XXXYIII. 

PIVOT-CAKEIAGES  OF  THE  THIRTY  SPANISH  GUNBOATS. 
(SEE   PLATE   58.) 


The  gim-carriages  .and  slides  constioicted  for  the  SpanisL 
gunboats  present  two  important  features  wliich  distinguisli 
the  same  from  other  pivot  systems — viz.,  the  slide  is  made 
to  rotate  round  a  permanent  central  fighting-bolt  secured  in 
the  middle  of  the  deck  near  the  bow  ;  consequently,  as  the 
bulwarks  of  the  Sj^anish  gunboats  are  low  enough  to  admit 
of  firing  en  barbette,  a  horizontal  range  of  240  deg.  is  ob- 
tained. 

The  other  important  feature  of  the  new  system  is  that 
of  enabling  the  gunner  to  apply  and  relieve  the  compressor 
instantaneously. 

Naval  artillerists  are  well  aware  of  the  advantage  of  ro- 
tating slides,  but,  owing  to  the  circumstance  that  such  an 
arrangement  unavoidably  carries  the  fighting-bolt  in  the  rear 
of  the  trunnion  when  the  gun  is  run  out,  such  slides  have 
been  deemed  impracticalde.      Evidently,   if   the  fighting-bolt 


CHAP.  XXXVIII.        SJ'AXl:sn  GUNBOAT  riVOT-CAElilAGES.  511 

1h'  placed  tar  iu  the  rear  uf  the  truiaiioii,  the  slide  will  be 
lifted  upwards  with  great  viuleiiee  at  the  iustaut  of  discliarge. 
This  apparently  insuperable  difficulty  is  completely  overcome 
in  the  arrangement  now  under  consideration,  by  the  expe- 
dient of  raising  the  circular  ring  on  which  the  slide  turns 
about  one  inch  above  the  deck.  By  this  expedient  an  effi- 
cient abutment  will  be  obtained  for  restraiuins  the  loujri- 
tudiiial  movement  of  the  slide  in  all  jjosltions.  A  plate  at- 
tached to  the  front  transom  of  the  slide,  as  represented  by 
the  illustration  on  Plate  58,  extending  down  as  far  as  the 
bottom  of  the  ring,  thus  takes  the  [)lace  of  the  ordinary 
fighting-bolt.  The  central  pivot,  round  which  the  slide  re- 
volves, fits  so  loosely  in  the  socket  of  the  cross-plate  that 
the  whole  force  of  the  recoil  is  received  by  the  descending 
trausom-plate  and  the  edge  of  the  deck-ring.  The  latter  is 
sustained  by  a  circular  platform  of  boards  1  in.  thick,  se- 
cured to  the  deck,  and  flush  with  the  top  of  the  ring.  The 
front  transom  and  outside  circumference  of  the  deck-ring 
being  in  advance  of  the  centre  of  the  trunnion  of  the  gun 
when  run  out,  the  force  of  the  recoil,  iu  place  of  lifting, 
will  evidently  tend  to  depress,  the  slide.  Ample  experience 
in  working  the  slides  of  the  Spanish  gunboats  has  fully 
demonstrated  this  fact,  and  established  the  superiority  of 
the  rotating  slide  in  point  of  easy  handling  as  well  as  ex- 
tensive lateral  range. 

It  will  be  evident  on  reflection  that  a  very  slight  modi- 
fication will  adapt  the  rotating  slide  thus  described  to  broad- 
side firing.     Such  a  modification  was  made  in  December,  1869, 


512  SPANISH  GUKBOAT  PlVOT-VAlllilAGES.        chap,  xxxviil. 

iiud  tliu  slide  tLii«  modified,  together  with  its  carriage,  was 
presented  to  the  Ordnance  Bureau  for  trial.  A  100-pounder 
Purrott  rifle-guu  having  been  mounted  on  the  carriage,  Com- 
mander E.  Simpson  was  ordered  by  the  Chief  of  the  Bureau 
to  conduct  the  trial  on  board  the  U.  S.  steamer  Tallapoosa, 
during  a  run  from  New  York  to  Washington.  Commander 
Simpson's  report  of  this  trial  and  his  description  of  the 
new  arrangement  are  so  lucid  that  I  adopt  the  same  in 
preference  to  any  description  I  could  pen  : 

"  The  carriage  consists  of  a  slide  and  top-carriage,  con- 
structed of  wrought  iron.  The  slide  is  composed  of  two 
rails,  with  four  bolts  connecting  them  at  intervals  of  two 
feet.  The  heurters  consist  each  of  two  plates  of  half-inch 
iron^  between  which  are  placed  the  rollers  for  lateral  train. 
They  are  each  strengthened  by  two  castings  placed  between 
the  plates  near  the  rails,  those  at  the  rear  end  being  con- 
tinued up  nine  inches  above  the  rails,  to  Avhich  are  secured 
the  huffers  of  india-rubber,  designed  to  receive  the  recoil 
when  the  carriage  is  permitted  to  recoil  the  whole  length  of 
the  slide. 

"The  middle  of  the  slide  rests  on  a  rail  on  the  deck 
designed  to  support  it  at  that  point,  and  on  which  it  slides 
\vhen  training. 

"  The  slide  has  one  transom  half  way  of  its  length  riveted 
to  the  inner  sides  of  the  rails,  and  on  a  plane  six  inches  be- 
low their  upper  surface. 

"To  an  angle-iron  turned  up  from  the  rear  of  the  tran- 
som, and  rising  to  the  level  of  the  rails,  is  bolted  the  rear 


CHAP.  XXXVIII.        SrAMSn  GUXBOAT  PIVOT-CARIirAGES.  513 

vud  (if  the  frictiu)i-lHii;  six  inclics  wide  aud  inie  aiul  a  (quarter 
iiidu's  tliick,  wliicli  is  coutiuued  horizontally  to  the  forward 
lu'urter,  -where  it  is  bolted  to  a  castiiiLr,  after  jiassing  whicli 
it  inclines  downwards  gradually  to  the  i)iv(>t,  where  it  is 
secured  to  the  pivut-l)()lt   thn)UgIi  a   liole  in  its  end. 

"A  composition  rack  is  bolted  on  the  inside  of  the  riglit 
rail,  the  teeth  extending  above  the  level  of  the  rails. 

"The  carriage  rests  on  four  rollers  front  and  rear,  the 
former  of  18  inches  diameter,  the  latter  of  7  inches.  To 
the  inner  face  of  the  right  forward  roller  is  bolted  a  work- 
ing-wheel of  composition,  with  its  cogs  gearing  below  into 
the  rack  on  the  slide,  while  above  it  gears  into  a  [)inion 
on  a  shaft  which  lias  its  bearings  in  the  brackets  of  tlie 
carriage.  A  crank  is  attached  to  the  end  of  this  shaft  on 
the  right  side  of  the  carriage,  and  by  it  the  carriage  is  run 
in  and  out  on  the  slide.  This  shaft  has  a  longitudinal  mo- 
tion, which  allows  the  pinion  to  be  geared  or  ungeart'il  at 
pleasure.  It  is  always  desirable  to  ungear  before  iirinii\  in 
order  to  prevent  motion  of  the  crank,  which  might  i)rove 
dangerous  to  the  gun's  crew. 

"  A  conveniently-arranged  clutch  holds  the  shaft  in  either 
position. 

"The  carriage  has  one  transom,  from  the  forward  i)ai-t 
of  which  project  two  arms,  one-third  the  width  of  the  tran- 
som apart,  extending  to  a  length  of  20  inches,  and  termi- 
nating in  eyes,  through  which  the  compression-shaft  passes, 
which  has  bearings  in  the  lower  part  of  the  brackets  and 
well  forward  of  the  forward  axle  of  the  carriage. 


514  SPANISH  GUKBOAT  PirOT-CAinHAGES.        chap,  xxxvm. 

"Under  the  friction-bar  is  a  clamp  17  inches  long  and 
6  and  10  inches  wide,  which  binds  against  the  under  face 
of  the  bar.  The  compression  is  produced  through  the  ec- 
centric motion  of  a  third  piece  resting  on  the  uj)per  clamp, 
a  side-elevation  of  which  represents  a  half-circle,  and  which 
is  fitted  over  the  compression-shaft.  This  eccentric  piece  is 
connected  with  the  friction-clamps  by  two  iron  straps,  with 
nuts  screwed  on  the  lower  ends  of  them.  It  will  be  per- 
ceived that  the  friction-clamps  occupy  a  position  in  the 
centre  line  of  the  carriage  and  between  the  ends  of  the 
two  arms  projecting  from  the  transom.  The  friction-clamps 
are  lined  with  hard  wood,  which  forms  the  surfaces  bind- 
ing on  the  friction-bar.  The  compression-shaft  has  its  bear- 
ings on  the  brackets  of  the  carriage,  and  projects  far  enough 
outside  the  left  bracket  to  receive  a  long  lever  which  is 
shipped  on  its  end,  and  which  has  a  vertical  motion,  limited 
by  the  adjustment  of  the  screw-nuts  on  the  ends  of  the 
iron  straps  which  connect  the  friction-clamj^s.  This  lever 
is  held  in  position  by  a  rack  on  the  outside  of  the  left 
bracket  when  the  required  compression  is  attained.  A  steel 
spring  at  the  lower  end  of  the  lever  binds  it  against  the 
bracket,  and  a  very  convenient  eccentric  arrangement  at  the 
handle  of  the  lever  enables  this  pressure  to  be  overcome 
when  desiring  to  move  the  lever." 

Having  prefixed  this  very  clear  and  precise  description 
to  his  report,  Commander  Simpson  proceeds:  "During  the 
firing  thus  tabulated,  the  running-oiit  gear  was  but  seldom 
used,   the  carriage   being   allowed  to    move   obedient   to    the 


CHAP.  XXXVIII.        SPAXISir  GUXBOAT  nrOT-OAEEIAGES.  515 

roll  of  the  vessel,  and  its  motiou  was  found  to  be  perfectly 
under  the  control  of  one  man  at  the  compression-lever,  who 
could  check  it  at  any  point.  The  compression  being  found 
to  work  well  in  deliberate  fire,  thirty  rounds  were  fired  to 
test  the  point  whether  rapid  fire  would  cause  the  heating 
of  the  friction-bar.  The  thirty  rounds  consumed  nearly 
thirty  minutes  in  firing,  at  the  end  of  which  time  the  tem- 
perature of  the  bar  was  slightly  raised,  but  in  no  way  inter- 
fei-cd  \\ith  a  continuance  of  firing.  Very  rajtid  firing  may 
be  done  with  this  carriage;  the  time  consumed  in  firing  the 
thirty  rounds  above  mentioned  was  in  consequence  of  the 
crew  not  being  accustomed  to  gun-exercise. 

"The  most  promiiR'nt  advantage — in  fact,  the  essential 
characteristic — of  this  carriage  is  its  system  of  compression, 
wliich  is  complete  and  instantaneous. 

"The  compression  in  use  Avith  our  pivot-guns  and  with 
our  turret-guns  invohes  the  use  of  a  screw,  which  requires 
time  to  work  ;  the  substitute  provided  in  this  carriage  is  a 
simple  motion  in  a  vertical  plane  of  a  lever,  which  is  in- 
stantaneous in  action,  and  quite  as  effective  in  its  result. 

"The  tardiness  of  action  in  the  compression  of  our  tuiret- 
guns  may  often  cause  hesitancy  in  casting  them  loose  in  a  sea- 
way, when,  with  a  more  speedy  means  of  compression,  they 
might  be  made  of  service.  The  slow  and  imperfect  action 
of  the  compressoi-s  fitted  to  our  pivot-guns  renders  necessaiy 
eccentric  rollei-s  to  the  axles,  so  that  the  carriage  may  be  let 
down  on  the  slide,  to  increase,  by  the  increased  surface  in 
contact,  the  friction  that  the  compressors  do  not  supply. 


516  SPANISH  GUNBOAT  PiVOT-CAEEIAGES.       chap,  xxxviii. 

"The  system  of  compression  doav  under  consideration  ad- 
mits of  keeping  tlie  carriage  always  on  its  rollers,  thus 
simplifying  tlie  mechanism  of  the  carriage,  and  dispensing 
with  the  levers  which  are  now  necessary  to  bring  the  rollers 
in  and  out  of  action.  The  four  men  now  devoted  to  this 
duty  could  be  dispensed  with. 

"  During  the  experiments  here  reeoixled  the  carriage  has 
fulfilled  the  advantages  claimed  for  it  by  its  inventor,  and, 
unless  subsequent  experiments  or  the  experience  of  actual 
service  should  develop  defects  not  now  apparent,  its  claim 
for  preference  over  any  carriages  now  in  use  in  the  navy 
must  be  allowed. 

"  During  the  firing,  the  shortest  distance  at  which  the 
recoil  was  checked  was  2  feet  5  inches,  which  was  only 
half  the  recoil  that  would  be  required  in  service  so  as  to 
have  the  gun  in  position  for  loading.  If  less  recoil  were 
required  at  any  time,  it  can  be  obtained  by  a  change  in  the 
adjustment  of  the  screw-nuts  on  the  strap  binding  the  fric- 
tion-clamjx"  * 

*  It  will  be  proper  to  notice  that  the  new  system  has  proved  so  successful  in 
practice  that  the  Spanish  Government,  in  addition  to  the  thirty  carriages  and  slides 
mounted  on  board  of  the  new  gunboats,  have  recently  ordered  several  sets  of  similar 
carriages  and  slides  for  other  vessels. 


CHAPTER   XXXIX. 

KOTAKY    GUX-CARRIAGE    AND   TRANSIT   rLATFORM. 

AP1>I.IED    TO    THE    SPANISH    GUNBOAT    TORNADO.* 

(SEE    PLATE    59.) 


Tin;  illustration  on  the  plate  referred  to  represents  a  new 
.system  of  transferring  the  battery  from  side  to  side,  witlK)nt 
resoiting  to  the  complicated  method  of  pivoting  practised 
in  our  ve.ssels  of  war.  In  addition  to  the  advantage  of  rapidly 
transfen-ing  the  guns  from  side  to  side,  an  all-r<aind  lii-e  is 
also  secured  by  this  system,  as  will  be  seen  by  the  following 
description  : 

The  leading  feature  of  the  device  is  that  of  placing  the 
gun-carriage  and  its  rotary  slide  on  a  circular  platform,  sup- 
ported on  four  cylindrical  rollei-s  (partially  shown  at  //) 
provided    with    flanges  like   those  of   the   wheels  of   railwjiy 

•  It  will  be  remembered  that  in  1873  this  gimboat.  Bftcr  a  spirited  chase,  cap- 
tured the  American  steamer  Virginia,  having  on  board  a  company  of  "  Cuban 
patriots"  and  war  material  intended  for  the  Cuban  insurgents.  The  capture  of  this 
vessel,  it  will  also  lie  remembered,  very  nearly  led  to  a  war  between  the  United  States 
and  Spain. 

617 


518  BOTABY  GUN-CARBIAGE  AND  PLATFOBM.     cn.\p.  xxxix. 

carriages.  These  rollers,  the  axles  of  wliicli  turn  in  appro- 
priate bearings  under  the  platform,  move  on  two  flat  pai'allel 
bronze  rails,  I  and  m,  secured  to  the  deck  at  right  angles  to 
the  line  of  keel.  One  of  these  rails,  w,  is  provided  with 
cogs  on  the  outside,  thus  forming  a  toothed  rack.  A  small 
horizontal  cog-wheel  under  the  platform  is  geared  into  the 
said  rack,  and  actuated  by  a  set  of  cog-wheels  arranged  as 
in  ordinary  lifting-jacks.  The  gear  is  put  in  motion  by  a 
vertical  spindle  having  a  hand-wheel  attached  to  its  ujiper 
end,  the  lower  end  being  made  to  fit  a  square  socket,  n, 
formed  in  the  axle  of  the  actuating  pinion  of  the  gear.  It 
is  hardly  necessary  to  observe  that  after  having  transferred 
the  2^kitform  to  the  desired  position,  the  vertical  spindle 
should  be  lifted  out  of  its  socket  and  removed,  in  order  not 
to  interfere  with  the  free  rotation  of  the  slide.  It  may  be 
mentioned  that  in  addition  to  the  gear  referred  to,  suitable 
eyebolts  are  ajiplied  to  admit  of  employing  ordinary  tackle 
in  transferring  the  platform  from  side  to  side.  Having  been 
I'olled  into  position  on  the  fighting  side  of  the  vessel — say 
starboard — the  platform  must,  of  course,  be  secured  by  two 
fighting-bolts.  One  of  these  is  seen  at  Tc,  the  second  of  the 
pair  being  concealed  by  the  slide.  On  rolling  the  platform 
to  port,  after  having  removed  the  fighting-bolts,  the  latter 
will  be  inserted  through  the  bolt-holes  of  the  lugs  g  on  the 
opposite  side  of  the  platform.  It  should  be  observed  that 
in  housing  the  gun  the  fighting-bolts  will  occupy  diagonal 
positions — plates,  as  shown  at  1c,  being  inserted  in  the  deck 
accordingly. 


cu.vr.  xxxix.      BOTAEY  CVK-CAKinAGE  AND  PLATFOUM.  519 

It   was  pointed   out  in   the  previous  chapter  tliat   if   the 
force  of  the  recoil  were  brought  to  bear  on  the  central  pivot 
round   which   the  slide    revolves,  the  latter  would  be   lifted 
uj.  violently,  or  seriously  jarred  at  the  instant  of  discharg- 
ing   the   gun,,    since    the    vertical    line,    passing   through    the 
centre  of  the  trunnion,  is  far  in  advance  of  the  central  pivot 
when   the   gun   is   rolled   out.     To   prevent   such   lifting   or 
jari-ing,  a  very  effective  expedient  has  been  resorted  to— viz., 
that    of   attaching   a    l)racket   d  at    the  forward   end  of   tlie 
slide,  extending  about  two  inches  below  its  base,  and  bearing 
fiimly  against  the  circumference  p  of  the  platform.     It  will 
be  readily  seen  that  if  the  bracket  referred  to,  which  acts 
as  a  hook,  be  placed  at  a  proper  distance,  while  the  pivot 
round   which    the    slide    turns  fits  loosely  in  its  socket,   the 
force  of  the  recoil  will  be  received   wholly  by  the  edge  2> 
of   the   platform,    at    the    point    where    the    bracket  d  bears. 
The   professional    reader   cannot  fail   to  perceive  the   advan- 
tage of  transferring  the  strain  from  the  central  pivot  in  rear 
of  the  trunnion  to  a  point  in  advance  of  the  same.     Obviously, 
the  practical  result  will   be  that  of  causing  the  carriage  and 
slide   to  bear  down  against   the   platform,   instead  of   being 
violently  jarred  or  lifted  up,  as  it  would  be  if  the  force  of 
the  recoil  were  brought  to  bear  on  the  central  pivot.     Re- 
garding the  proper  position  of  the  fighting-bolts  for  securing 
the  platform  during  firing,  it  will  be  evident  that  if  inserted 
at  I;   as  shown   (for  the  sake  of  ready  explanation)  in  the 
illustration,   the   platform  would   be  lifted  or  jarred  at  the 
moment  of  discharging  the  gun;  while  by  inserting  the  fight- 


520  IWTABY  GUN-CARRIAGE  AND  PLATFORM,     chap,  xxxix. 

iug-l>()lt  at  <j  the  teudeucy  will  be  to  depress  the  platform, 
thereby  securing  perfect  repose  throughout  the  eutire  struc- 
tui-e. 

The  gun-carriage  itself  having  been  minutely  described 
in  Chap.  XXXVIII.,  it  will  only  be  necessary  to  observe 
that  the  friction-bar  c,  which  in  the  carriage  referi'ed  to  was 
made  of  iron,  has  been  made  of  bronze  in  all  the  recent 
carriages  constructed  under  my  patents.  It  was  found  in 
practice  that  the  application  of  oil  or  grease  to  this  bar, 
indispensable  to  prevent  its  corrosion,  considerably  diminished 
the  friction — a  circumstance  of  no  importance  if  the  dimi- 
nution had  been  constant  in  amount ;  but  the  lubricating 
medium,  varying  in  quantitj-,  obviously  causes  irregularity  in 
the  intensity  of  the  required  friction.  Bronze  being  now 
substituted  for  iron,  renders  the  application  of  grease  un- 
necessary ;  hence  the  friction  between  the  wooden  lining  of 
the  clamp  h  and  the  bar  c  becomes  uniform.  Accordingly, 
by  pushing  the  hand-lever  a  to  a  given  notch  of  the  circular 
tooth-rack  s,  it  has  been  found  that  the  length  of  the  recoil 
may  be  regulated  with  remarkable  accuracy. 


CHAPTER   XL. 

GUN-CAKRIAGE  FOR  COAST  DEFENCE. 
(SEE   PLATE   60.) 


Engineering  of  March  20,  1872,  published  the  following 
article,  headed  "  Coast  Defence  "  : 

"  The  problem  of  how  best  to  defend  our  coasts  has  of 
late  attracted  so  much  attention  that  the  illustration  which 
we  publish,  representing  a  gun-caniage  forming  part  of  a 
new  system  of  coast  defence  planned  by  Captain  Ericsson, 
will  possess  special  interest.  The  gun  is  mounted  behind 
an  inclined  movable  shield  of  solid  plate  iron,  4  ft.  high 
above  the  parapet,  so  arranged  that  the  muzzle  is  unmasked 
at  the  moment  of  firing,  the  shield  affording  protection  against 
projectiles  striking  above  the  parapet.  It  is  asserted  that  this 
plan  is  more  efficient  than  that  of  Moncrieff ;  but,  as  it  is  not 
our  intention  at  present  to  institute  a  comparison  between 
the  rival  systems,  we  proceed  at  once  to  describe  the  illus- 
trated carriage  (see  Plate   60).     The    recoil    is   checked   by 


522 


OUN-CARRIAGE  FOB  COAST  DEFENCE.         chap.  xl. 


friction  produced  by  clamping  two  longitudinal  Lars  secured 
in  tlie  middle  of  the  slide,  tlie  compression  being  effected  by 
a  transverse  axle,  on  the  principle  adopted  in  the  Princeton 
carriage.  The  longitudinal  bars,  however,  are  composed  of 
bronze  in  place  of  wood.  The  friction-clamp  (a  longitudinal 
section  of  which,  through  the  vertical  plane,  will  be  found 
represented  in  the  accompanying  delineation  is  firmly  attached 
to  the  front  of  the  carriage.      The  faces  of  the  fiictiou-bars 


being  smooth  and  true,  and  the  wooden  linings  of  the  clamp 
accurately  fitted,  it  will  be  perceived  that  a  very  slight  move- 
ment of  the  upper  and  lower  parts  towards  each  other,  after 
contact  with  the  bars,  will  at  once  cause  friction,  provided 
that  the  set-nuts  of  the  clamp-cap  have  been  properly  tight- 
ened. In  order  to  comprehend  correctly  this  peculiar  system 
of  compression,  let  us  suppose  that  the  clamp,  as  well  as 
the  bolts  which  hold  the  same  together,  are  perfectly  rigid, 
and  that  the  transverse  axle  is  flattened  so  as  to  make  it  but 
slightly  oval.     Turning  the  latter  through  an  arc  of  90  deg. 


CHAP.  XL.  GUK-CABEIAGE  FOJi  COAST  DEFENCE.  523 

will,  uinlt'i-  these  conditions,  obviously  produce  an  enoraious 
pressure.  It  Las  been  objected  that,  if  the  axle  is  but  slightly 
oval,  the  wear  of  the  wooden  linings  and  the  faces  of  the 
frictiou-bai-s  will  soon  destroy  the  efficacy  of  the  compres- 
sion. To  meet  this  objection  the  constructor  has  placed  the 
clamp  conveniently  in  front  of  the  carriage,  in  order  that  the 
set-nuts  may  readily  be  screwed  down  whenever  rei^uired. 
Practice,  it  appears,  has  shown  that  the  wear  is  insignificant 
with  friction-bars  composed  of  bronze.  Iron  bai-s,  on  the 
other  hand,  owing  to  corrosion  and  consequent  abrasion,  tend 
to  cut  the  wooden  lining  unless  grease  be  applied — an  expe- 
dient inadmissible,  as  it  greatly  diminishes  the  desired  adhe- 
sion, besides  rendering  the  same  very  irregular.  It  will  he 
seen  in  the  illustration  on  Plate  6()  that  the  hand-lever  by 
means  of  which  the  compi-ession  is  applied  or  relieved  is  held 
in  position  by  a  segment  (provided  with  notches)  attached 
to  the  side  of  the  carriage;  while  a  spring  secured  to  the 
end  of  the  transverse  axle  presses  against  the  outside  of  the 
lever,  thereby  preventing  the  same  from  leaving  the  notches 
dming  the  recoil  of  the  gun. 

"  Captain  Ericsson's  ])lan  of  employing  a  series  of  friction- 
bai"s  one  above  the  other,  or  placed  side  by  side,  as  in  the 
monitoi-s,  appropriately  termed  the  '  multiplex  system,'  copied 
by  Captain  Scott,  Sir  William  Armstrong,  and  othei-s,  involves 
a  paradox  ^\•hic•h  merits  special  notice — viz.,  tliat  without 
employing  additional  force,  any  amount  of  friction  may  be 
produced.  It  \vill  be  evident  on  reflection  that  whatever 
number  of  bars  be  employed,  the  friction  between  the  face 


534  GUN-CAEEIAGi:  FOB  COAST  DEFENCE.         chap,  xl, 

of  eacli  and  the  face  of  the  clamp  will  depend  solely  on 
the  pressure  applied.  Hence,  if  four  bars,  presenting  eight 
surfaces,  be  employed,  the  retarding  force  opposing  the  recoil 
of  the  gun  will  be  quadruple  that  of  one  bar  presenting 
two  surfaces.  With  reference  to  running  out  the  gun,  the 
following  explanation  will  suffice :  The  forward  tracks,  situ- 
ated somewhat  in  advance  of  the  trunnion,  are  keyed  to  an 
axle  supj)orted  by  bearings  in  the  side  frames  of  the  carriage. 
A  cog-wheel  is  attached  to  the  said  axle,  into  which  a  small 
pinion,  operated  by  an  ordinaiy  crank-handle,  is  geared. 

"  Before  adverting  to  the  mechanism  of  the  slide,  it  will 
be  well  to  observe  that  light  gear  of  small  multiplying  power 
Avill  answer  for  training,  since  the  movement  is  always  in 
the  horizontal  plane.  It  will  be  noticed  that  the  exterior 
segment  is  provided  with  a  projecting  rack  in  the  middle 
— an  expedient  which  overcomes  the  difficulty  so  frequently 
experienced  on  the  old  plan  of  employing  separate  racks, 
that  settlement  of  the  segment  on  which  the  rollers  run 
occasions  binding  between  the  cogs  of  the  driving-pinion 
and  those  of  the  rack.  It  is  scarcely  necessary  to  remark 
that  the  rollers  applied  on  the  opposite  sides  of  the  toothed 
projection  of  the  exterior  segment  turn  freely  on  the  axle 
to  which  the  driving-pinion  and  the  vertical  conical  wheel 
are  attached.  The  action  of  the  small  conical  pinion  geared 
into  the  wheel  mentioned,  operated  by  means  of  the  hori- 
zontal hand-wheel,  requires  no  explanation." 


CHAPTER   XLI. 

THE  THIRTY  SPANISH  GUNBOATS  AND  THEIR  ENGINES. 
(SEE   PLATK   61.) 


The  material  aid  which  the  Cuban  insurrection  derived 
from  outside  sources  compelled  the  Spanish  Government  in 
1809  to  build  a  fleet  of  swift  gunboats  to  form  a  cordon 
round  the  island  jis  the  only  means  of  preventing  blockade- 
runners  from  conveying  men  and  warlike  stores  to  the  insur- 
gents. Admiral  Malcampo,  naval  commander  in  Cuba,  was 
accordingly  instructed  by  his  Government  to  procure  the 
needed  vessels  in  the  United  States.  The  Admiral  succeeded 
in  canying  out  his  instructions  with  extraordinary  prompt- 
ness, as  will  be  seen  from  the  following  concise  statement, 
copied  from  the  Army  and  Navy  Journal  of  Isovember  20, 
1869: 

"  The  annals  of  naval  construction  probably  furnish  no 
instance  of  greater  diligence  than  that  displayed  in  the  pro- 
duction of  the  thiity  Spanish  gunboats  now  floating  on  the 


52G  SPAXISE  GUNBOATS  AND  THEIR  EN6TXES.         chap.  xli. 

Hudson.  Tlie  planning  Laving  been  entrusted  to  Captain 
Ericsson,  the  contract  for  building  the  fleet  was  entered  into 
with  the  Delamater  Iron- Works,  in  this  city,  on  the  3d  of 
May,  1869.  On  the  19th  of  May  the  fii-st  keel  was  laid, 
and  on  the  23d  of  June  the  first  vessel  was  launched  from 
Pouillon's  ship-yard — thirty-four  working  days  after  laying 
the  keel.  September  3 — just  four  months  from  the  signing 
of  the  contract,  and  three  months  and  sixteen  days  after  lay- 
ing the  first  keel — the  last  vessel  of  this  fleet  was  launched, 
at  which  time  fifteen  of  the  vessels  previously  launched  had 
engines  and  boilers  on  board ! 

"  The  Spanish  gunboats  are  sea-going  twin-screw  vessels, 
107  feet  long  on  the  water-line,  22  feet  6  inches  extreme 
beam,  8  feet  depth  of  hold,  and  draw  4  feet  11  inches  when 
fully  equipped  for  service,  with  coal,  stores,  and  ammunition 
for  100  rounds  on  board.  The  lines  at  the  bow  are  some- 
what full,  in  order  to  sustain  a  heavy  bow  gun,  the  breadth 
of  the  deck  being  carried  well  forward  for  the  purpose  of 
facilitating  the  manipulation  of  this  gun,  of  which  we  will 
speak  presently.  The  run  is  very  clean,  the  lines  being 
deemed  faultless  for  a  t\vin-screw  vessel.  The  construction 
of  the  hull  presents  two  novelties  ^vorthy  of  special  mention. 
The  apparently  insoluble  character  of  the  problem — a  gun- 
boat of  this  class  drawing  only  59  inches  of  water  when  fully 
equipped  for  service — compelled  the  designer  to  dispense  with 
the  keel.  Shipbuilders,  it  appears,  at  first  objected  to  this 
innovation,  but  now  admit  that  these  gunboats  may  take 
ground    with    far    less    risk    of    straining    and    leaking    than 


CUAP.  XLI.        SPANISU  GUyBOATH  AM)  THElIi  EyOINES.  527 

oriliiiary  liglit-ilrauglit  vessels  witli  their  weak  keels.  The 
other  novelty  iilliuled  to  is  the  cutting  down  the  rail  and 
substituting  a  low,  heavy  tindjer  bulwark  at  the  Ijow,  pro- 
vided with  substantial  \vater-ways  and  lined  with  sheet-iron 
to  admit  of  firing  the  gun  e/i  barbette. 

"In  addition  to  their  ample  steam-power,  the  Spanish 
gunboats  carry  full  amount  of  canvas,  being  schooner-rigged, 
with  yard  and  square-sail  on  the  foremast.  "Wire-rigging 
having  been  adopted,  and  the  masts  and  smoke-pipe  raked 
more  than  usual,  the  appearance  of  these  twin-screw  vessels 
is  peculiarly  light  and  saucy.  Considering  their  great  num- 
ber, swiftness,  light  draught,  and  the  long  range  of  their 
guns,  it  is  evident  that  the  Spaniards  will  l,e  enal)led  iov 
the  future  to  prevent  ett'ectually  incursions  un  the  Cuban 
coast. 

"As  might  be  expected,  the  .steam  ntachiiiery  of  these 
novel  war-vessels  presents  features  of  special  interest  (see 
illustration  on  Plate  Gl).  It  has  frequently  been  urged  as 
an  ol)jection  against  the  twin-screw  system  that  the  double 
set  of  engines,  four  steam-cylinders,  with  duplicates  of  all 
their  working  parts,  called  for  in  this  system,  render  the 
whole  too  complicated  and  heavy  for  small  vessels ;  prevent- 
ing at  the  same  time  the  application  of  ■surface-comhnsation. 
The  designer  has  overcome  these  objections  by  inti-oduciug 
a  surface-condenser  which,  while  it  pei-forms  the  function  of 
condensing  the  steam  to  be  returned  to  the  boiler  in  the 
form  of  fresh  water,  serves  as  the  principal  support  "of  the 
engines,  disjjensing  entirely  with   the  usual  frame-work.     Be- 


528  SPANISH  GUNBOATS  AND  THEIB  ENGINES.        chap.  xli. 

sides  this  expedient,  eacli  pair  of  cylinders  have  their  slide 
frames  for  guiding  the  movement  of  the  piston-rods  cast  in 
one  piece.  Altogether,  the  combination  is  such  that  the  total 
weight  and  the  space  occupied  by  these  novel  tvsdn-screw 
engines  do  not  exceed  the  ordinary  single-screw  engines  of 
equal  power.  Several  improvements  connected  with  the 
Avorking-gear  have  also  been  introduced.  The  outer  bear- 
ings of  the  propeller-shafts,  always  difficult  to  regulate  and 
keep  in  order  on  the  twin-screw  system,  are  self-adjusting, 
and  accommodate  themselves  to  every  change  of  the  direc- 
tion of  the  shafts.  This  is  effected  by  their  being  spherical 
externally,  and  resting  in  corresponding  cavities  in  the  stern 
braces  or  hangers.  The  'spring-bearings,'  for  supporting  the 
middle  of  the  shafts,  are  also  arranged  on  a  similai'  self- 
adjusting  principle.  The  thrust-bearing,  which  receives  the 
pressure  of  the  propeller,  is  a  peculiar  construction,  the 
arrangement  being  such  that  the  bearing  surfaces  remain  in 
perfect  contact,  however  much  the  shaft  may  be  out  of  line. 
The  reversing-gear,  likewise,  is  quite  peculiar,  insuring  com- 
plete control  over  the  movement  of  the  two  propellers  under 
all  circumstances.  It  is  claimed  that  these  engines  are  the 
lightest  and  most  compact  yet  constructed  for  twin-screw 
vessels. 

"  The  internal  arrangements  and  fittings  show  thorough 
knowledge  and  experience  on  the  part  of  the  superintending 
officer.  Our  friends  on  the  Baltic,  who  pride  themselves  on 
knowing  moi-e  about  gunboats  than  other  nations,  will  be 
astonished  when  they  learn  how  the  Spaniards  fit  out  such 


CHAP.  XLI.        SPANISH  GUNBOATS  AND  IHEIB  ENGINES.  529 

vessels.     Indeed,    tlio   e«iuipmeiit    more    resembles    that   of    a 
yacht   than    that   needed    for   a   plain   gunboat.     We  cannot 
afford    space   for    a    specification,    and    therefore    proceed    to 
notice   only  that   which  is  essential.     The    coal-bunkers    are 
placed  on  each  side  of  the  boiler,  extending  equally  forw  aid 
and  aft  of  the  centre  of  displacement  of  the  vessel,  in  order 
to   preserve    pei-fect   trim,   whether  the  bunkers   are   full    or 
empty.     The  magazine,   located   in   the  centre    of   the    vessel 
between    the    engine-room    and    the    officers'    quartei-s   aft,    is 
lined  with  lead  on  the  inside,  with  the  unusual  precaution 
of   having   the   outside   protected   by  sheet-iron.      There   are 
three   distinct    modes   of   flooding  this   magazine — viz.,   from 
the  sea,  by  a  powerful  hand-pump,  and  by  the  donkey-engine 
pump.     In    addition   to   the   ordinary   water-tanks,   a   'fresh- 
water maker'  of  ample  capacity  is   provided,  in  which  the 
condensation  of  the  steam  is  effected  by  the  current  of  sea- 
water  which  passes  through  the  surface-condenser;  the  fresh 
water  being  drawn   off   through   a   bent -pipe   on   deck.     A 
combined  capstan  and   mndlass   of   novel  construction,  suffi- 
ciently  low   to   fire   over,   is   bolted   to   the   deck    over    the 
chain-locker   at   the   bow,   the   combination   being  such  that 
the   capstan   may   be    used    alone,   or   one   or  both   anchoi-s 
raised  at  the  same  time. 

"Respecting  the  armament,  the  following  brief  notice 
must  suffice  for  the  present:  It  consists  of  a  100-pound  rifle- 
gun  placed  at  the  bow— a  Pari-ott  rifle— but  a  very  different 
weapon  from  that  represented  by  the  photographed  frag- 
ments which  embellish  so  many  pages  of  General  Gillmore's 


530  SPANISH  GUNBOATS  AND  TEEIB  ENGINES.        chap.  XLl. 

famous  book.  Briefly,  it  is  an  improved  Panott  100-j)oim(l 
rifle,  witli  wrouglit-iron  hoops  round  the  chamber,  cariied  to 
within  three  inches  of  the  trunnion,  the  chase  being  increased 
to  correspond  with  the  increased  strength  attained  by  the 
extension  of  the  re-enforce.  The  severe  ordeal  through  which 
the  improved  gun  has  passed  during  recent  trials  at  Cold 
Spring,  conducted  by  the  Spanish  officers,  promises  so  well 
that  no  doubt  this  improved  Parrott  gun  has  a  future. 

"  Of  Captain  Ericsson's  new  gun-carriage — on  which  the 
improved  gun  is  mounted — one  of  the  leading  features  of 
the  Spanish  gunboats,  we  have  space  for  only  a  cursory  no- 
tice. It  will  be  inferred  from  what  has  already  been  stated 
that  the  intention  is  to  fire  over  the  bow  and  in  line  with 
the  keel.  For  this  purpose,  and  in  order  to  command  a  wide 
horizontal  range,  a  circular  platform  of  wood,  surrounded  by 
a  brass  ring  of  12  feet  6  inches  diameter,  is  bolted  to  the 
deck  at  the  bow.  The  gun-slide,  composed  of  wrought  iron, 
provided  with  friction-rollers  at  both  ends,  rotates  round  a 
pivot  secured  to  the  deck,  in  the  centre  of  the  said  brass 
ring.  The  carriage  is  made  of  light  wrought-iron  plates  and 
angle-iron,  riveted  together  in  such  a  manner  as  to  ensure 
great  strength  longitudinally  as  well  as  transversely."  (See 
illustration  of  gun-carriage  on  Plate  59.) 

Having  described  the  internal  arrangements  of  the  Span- 
ish gunboats  somewhat  minutely,  the  Army  and  Navy 
Journal  concludes   its   notice   of  these   vessels   by   saying : 

"  A  fleet  of  thirty  war-vessels  precisely  alike  being  by 
no  means  an  ordinary  sight,  a  visit  to  Delamater's  works  on 


CHAP.  XLI.         SPAA'ISII  GUNBOATS  AND  TUEIE  ENGINES.  531 

the  Hudson  where  the  saucy-looking  craft  are  now  stationed, 
ten  abreast,  cannot  fail  to  be  very  interesting  to  naval  men. 
It  is  a  significant  fact  that  this  groat  display  of  offensive  and 
defensive  force  is  the  result  of  the  efforts  of  a  single  estab- 
lishment, directed  Ijy  individual  skill.  Evidence  more  con- 
clusive could  not  be  furnished  that  the  progress  of  the 
country  and  its  resoui-ces  are  equal  to  any  future  emer- 
gency.'' 


CHAPTER   XLII. 

A  NEW   SYSTEM   OF   NAVAL   ATTACK. 
(SEE   PLATE   62.) 


A  HEAVY  body  of  regular  form,  whose  density  is  greater 
tlian  that  of  atmosplieric  air,  moving  latei'ally  tlirough  the 
atmosphere,  is  inexorably  under  the  influence  of  the  earth's 
attraction,  and  therefore  describes  a  foreshortened  parabolic 
curve  during  its  flight ;  while  a  submerged  body,  the  weight 
of  which  is  equal  to  the  weight  of  the  water  it  displaces,  is 
not  affected  by  the  earth's  attraction ;  and  that  consequently, 
if  2)ut  in  motion  under  the  surface  of  a  quiescent  fluid  of  unli- 
mited extent,  such  a  body  will  continue  to  move  in  a  straight 
line  until  the  motive  energy  which  propels  it  becomes  less 
than  the  resisting  force  of  the  surroundins;  medium. 

In  virtue  of  the  first  part  of  this  general  proposition,  a 
heavy  body  may  be  projected  in  such  a  manner  that  the 
termination  of  its  trajectory  shall  make  any  desirable  angle, 
less  than  45  deg.,  with  the  horizontal  line,  independently  of 
the  length    of  the  chord  of  the  trajectory.     In  other  words, 

633 


CHAP.  XLII.        A    XEW  SYSTEM  OF  XAVAL  ATTACK.  533 

the  body  may  he  projected  at  variable  distances  over  water, 
and  yet  strike  its  surface  at  any  desirable  angle.  This 
important  result  is  effected  simply  by  varying  the  relative 
proportion  between  elevation  and  strength  of  charge.  The 
second  part  of  the  stated  general  prop(^sition  is  of  equal 
importance.  It  points  to  the  fact  that  the  ti-ajectory  may 
be  extended  in  a  straight  line  under  water,  to  any  desirable 
distance,  irrespective  of  the  speed  of  the  submerged  pro- 
jectile. Accordingly,  a  shot  may  be  projected  from  one 
vessel  towards  another  within  moderate  ranges  in  such  a 
manner  that  it  shall  dip  into  the  water  at  a  considerable 
distance  from,  or  close  to,  the  vessel  assailed,  independently 
of  the  distance  between  the  two  vessels.  Also,  that  the 
shot  may  be  projected  at  such  an  angle  that  the  pi-olono-a- 
tion  of  its  trajectory  in  a  straight  line,  after  contact  with 
the  water,  shall  strike  the  hull  of  the  vessel  assailed  at  any 
desirable  depth  below  the  surface. 

That  a  certain  relation  between  charge  and  elevation 
enables  us  to  project  a  spherical  shot  in  such  a  manner  as 
to  strike  the  water  at  any  desirable  distance  from  an  oppo- 
nent's vessel,  at  angles  within  45  deg.,  needs  no  further 
demonstration.  Hence,  if  the  trajectory  be  such  that  its 
e.xtension  in  a  straight  line  from  the  point  of  contact  with 
the  water  leads  to  the  hull  of  the  vessel  assailed,  the  latter 
will  be  hit — on  condition,  however,  that  the  shot  is  not  di- 
verted from  its  course  on  entering  the  water,  and  provided 
its  vis  viva  be  sufficient  to  overcome  the  resistance  encoim- 
teied   during   its    passage   through    the    water.      These    indis- 


534  A   NEW  SYSTEM  OF  NAVAL  ATTACK.        chap.  XLII. 

pensable  conditions,  especially  the  first-named,  wliicli  appa- 
rently cannot  be  complied  with,  show  the  ditficulty  of  hitting 
a  vessel  below  the  Avater-line.  And  if  we  suppose  that  the 
projectile  is  not  spherical,  another  serious  difficulty  presents 
itself.  An  elongated  body  will  not  bend  to  the  curvature 
of  the  trajectory  during  the  flight  through  the  air,  but  re- 
tain during  its  course  the  same  inclination  as  the  gun  from 
which  it  has  been  projected ;  hence  it  will  fall  nearly  flat 
on  the  surface  of  the  water  when  striking. 

Agreeably  to  our  general  proposition,  a  regular  body, 
weighing  as  much  as  the  water  it  displaces,  is  independent 
of  the  earth's  attraction ;  but  there  is  another  force  which, 
notwithstanding  the  absence  of  any  gravitating  tendency, 
will  cause  a  body  of  regular  form  moving  under  water  to 
deviate  from  a  straight  line  and  rise  to  the  surface.  A 
cone  moving  in  the  direction  of  its  apex  and  in  the  line 
of  its  axis  horizontally,  or  on  an  incline,  will,  owing  to  the 
inertia  and  the  nearly  incompressible  nature  of  water,  more 
readily  displace  the  column  which  rests  upon  and  depresses 
its  upper  half  than  the  column  from  below  with  its  lifting 
tendency.  Consequently,  the  course  of  the  conical  body 
will  be  diverted  from  the  straight  line  upwards,  describing 
a  curve  nearly  elliptical,  and  quite  sudden,  if  the  speed  be 
great.  A  cylinder  with  serai-spherical  ends  will,  from  the 
same  cause,  ascend  to  the  surface  if  moved  in  the  line  of 
its  axis  ;  while  a  cylinder  with  flat  ends  will  take  a  down- 
ward course,  gradually  increasing  its  inclination,  until  at  last 
the  axis  assumes  a  vertical  position.      Obviously,  the  lower 


CHAP.  XLII.        A  JV^ir  SYSTEM  OF  NAVAL  ATTACK.  535 

part  of  the  forward  flat  end  encountei"S  a  greater  resistance 
than  the  upper  part ;  hence  tlie  lower  half  of  the  transverse 
section  of  the  cylinder  suffers  an  excess  of  retardation,  which 
occasions  the  downward  course  described. 

The  question  whether  the  apparently  insuperable  diffi- 
culties thus  pointed  out  can  be  overcome  by  mechanical 
expedients,  has  occupied  my  attention  for  a  long  time ;  and 
numerous  experiments  have  been  made  to  test  the  efficacy 
of  certain  forms  suggested  by  theoretical  considerations. 
These  forms  being  correct,  the  direction  of  the  projectile 
during  its  flight  through  the  air  w^ll  be  parallel  with  the 
trajectory,  and  on  entering  the  water  it  will  not  be  diverted, 
but  continue  to  move  under  the  surface  with  the  same  incli- 
nation it  had  on  coming  in  contact  with  the  dense  medium. 

The  illustrations  on  Plate  62  present  the  main  features 
of  the  system  under  consideration  so  distinctly  that  it  will 
be  superfluous  to  enter  on  a  general  explanation  of  the 
nature  of  the  scheme.  It  should  be  stated,  however,  that 
the  elongated  projectile  is  charged  with  dynamite  or  gun- 
cotton,  and  provided  with  a  percussion-lock  at  the  for\vard 
end,  which  explodes  the  charge  by  contact.  It  may  be  men- 
tioned that  numerous  plans  have  been  suggested  during  the 
last  few  years  for  projecting  solid  shot  under  water,  for  the 
purpose  of  sinking  ships.  In  several  instances  these  plans 
have  been  carried  into  practice,  with  the  invariable  result 
that  the  resistance  of  the  water  has  been  found  so  great, 
even  at  short  distances,  that  an  ordinary  wooden  hull  has 
proved  to  be    impenetrable.     The   plan   now  uuder   conside- 


536  A  NHW  SYSTEM  OF  NAVAL  ATTACK.        chap.  xlii. 

ration  bears  uo  resemblance  to  these  projects,  since  tlie  force 
of  the  projectile  on  reaching  its  destination  need  only  be 
sufficient  to  actuate  the  trigger  which  causes  the  ignition  of 
the  explosive  charge. 

Apart  from  the  theoretical  considerations  relating  to  the 
course  of  elongated  projectiles  under  water,  the  practical 
question  of  motive  poiver  to  propel  the  same  claims  our 
attention.  It  is  hardly  necessary  to  state  that  the  force 
relied  upon  is  the  vis  viva  possessed  by  the  projectile  on 
coming  in  contact  ^vlth  the  water.  Before  estimating  this 
force,  it  will  be  proper  to  call  attention  to  the  fact  that 
the  new  system,  to  be  successful,  does  not  call  for  attack 
at  a  great  distance,  provided  the  vessel  from  which  the 
missile  is  projected  has  greater  speed  than  the  opponent,  and 
at  the  same  time  adequate  protection  against  his  artillery. 
Hence  the  destruction  of  the  vessel  assailed  would  be  as 
certain  if  the  distance  of  500  ft.  were  the  limit  as  if  a  range 
of  5,000  ft.  better  suited  the  new  system.  It  will  be  inferred 
from  this  explanation  that,  although  there  is  uo  special  limit 
Avithin  ordinary  ranges,  the  plan  is  to  attack  at  distances  not 
much  exceeding  500  feet,  unless  the  sea  be  very  smooth. 

The  vis  viva  of  a  projectile  15  in.  in  diameter,  of  such 
a  length  that  it  displaces  500  lbs.  of  water,  may  be  readily 
estimated  if  we  suppose  the  charge  of  powder  in  the  gun 
to  be  so  regulated  that  the  speed  on  entering  the  water  will 
be  400  ft.  per  second,  necessary  to  furnish  sufficient  motive 

power;  thus   -—  =  2500  X  500  =  1,250,000  ft.dbs.     A  cylin- 


CHAP.  XLii.        A  M:W  system  of  XAVAL  attack.  537 

(Iric'ul  body,  15  in.  in  diameter,  with  semi-splieiical  cuds, 
moving  at  a  rate  of  100  ft.  per  second  under  water,  requires 
a  constant  motive  force  of  somewhat  less  than  1,500  lbs. 
Assuming,  then,  that  the  projectile  passes  through  150  ft. 
of  water — the  mean  distance  represented  liy  tlie  diagram — 
we  have  a  resistance  of  150  X  1500  =  225,000  ft.-lbs.  to 
overcome.  The  motive  force,  it  will  thus  be  seen,  is  more 
than  five  times  greater  than  the  resistance;  consequently, 
no  doubt  can  be  raised  as  to  the  adequacy  of  the  motive 
power  furnished  by  the  vis  viva  of  the  projectile.  It  should 
be  observed  that  the  resistauce  is  very  great  at  first,  and 
that  the  speed  diminishes  in  a  very  rapid  ratio ;  but  it  would 
be  futile  to  present  a  formula  expressing  the  ratio  of  speed 
and  resistance,  since  the  form  of  the  body  (withheld  for 
obvious  reasons)  is  the  chief  element  in  the  calculation. 
Let  us  bear  in  mind  that,  while  the  resistauce  against  a 
blunt  body  is  exceedingly  great,  one  provided  with  a  sharp 
point  readily  enters  the  \vater,  even  at  the  rate  of  400  ft. 
per  second. 

With  reference  to  the  gun,  it  should  be  mentioned  that 
the  very  low  speed  of  the  pix)jectile,  and  the  consequent 
small  charge  of  powder  needed,  render  heavy  metal  unneces- 
sary. Besides,  slow-burning  cake-powder,  contained  in  cellu- 
lar caitridges,  will  be  emph)yed,  in  order  to  check  rapid 
ignition,  and  in  order  to  sustain  a  unifonn  pressure  duiing 
the  discharge.  By  reference  to  our  illustration,  it  will  be 
seen  that  the  guns  are  loaded  from  below,  and  for  that  pur- 
pose so   ari'anged    as    to    admit    of    lacing    depressed  GO  deg. 


538  A   Ni:W  SYSTEM  OF  NAVAL  ATTACK.        chap.  xlii. 

Gnu-carriages  are  dispensed  with,  the  trnuuious  being  sns- 
peuded  by  adjnstable  pemlnlum-links  secured  under  the 
turret-roof.  The  recoil  is  checked  by  buffers  attaclied  to 
the  turret  wall  in  rear  of  the  breach. 

It  is  jiroper  to  state  that  the  method  of  loading  guns 
from  below  deck,  as  shown  in  our  illustration,  was  planned 
by  me,  and  drawings  of  the  same  exhibited  in  New  York 
several  years  before  it  was  claimed  by  certain  American 
engineers  as  their  invention. 

Respecting  the  safety  of  the  charge  in  the  shell  from 
ignition  during  the  discharge,  it  should  be  observed  that 
recent  impi'ovements  in  torpedo  practice  effectually  prevent 
such  accidents.  With  reference  to  the  calibre,  it  is  evident 
that  this  system  of  attack  calls  for  dimensions  that  Avill 
admit  a  projectile  of  sufficient  capacity  to  contain  a  charge 
which,  by  its  explosion,  will  destroy  a  first-class  ship  of  war 
built  on  the  cellular  plan.  Nothing  short  of  15-iu.  calibre 
will  answer  for  this  purpose.  The  American  and  Swedish 
15-in.  guns  are  admirably  calculated  for  the  purpose,  although 
they  are  unnecessarily  heavy. 

European  savants,  especially  certain  Swedish  naval  artil- 
lerists, who  have  criticised  my  advocacy  of  the  15-in.  guns, 
\vill  understand,  on  looking  into  this  matter,  \\\\y  I  have 
persisted  in  advising  the  Scandinavians  to  cai'ry  tliis  large 
calibre  in  their  monitor  turrets  as  the  most  effective  weajjon 
against  their  powerful  neighbors.  Assuredly  the  Danes  will 
have  no  cause  to  fear  tlie  Prussian  Konhj  Willielm  or 
FrkdricJi   der    Grosse,    should    their    ports    be    defended    by 


CHAP.  xi.n.        A  XEW  SYSTEM  OF  XAVAL  ATTACK.  539 

vessels  aniieil  witli  guns,  l)y  means  of  uliirh  sfvcral  liiindivd 
pounds  of  dynamite  or  gun-t't)tt()U  could  be  exploded  under 
the  hulls  of  the  intruders. 

Tlie  important  question  of  hitting  tlie  intended  <)l)Ject 
will  be  best  answered  by  a  eareful  examination  of  the  illus- 
tration, wliieli  eannot  fail  to  convince  experts  that,  in  mode- 
rate weather,  the  proposed  projectile  may  be  made  to  dip 
at  the  pro[>er  distance  fi'om  the  opponent's  vessel.  The 
different  [)arabolic  curves  marked  on  tlie  delineations  on 
Plate  62  clearly  show  that  no  great  accuracy  is  called  for, 
and  that  the  projectile  may  dip  at  various  distances  from 
the  vessel  assailed,  and  yet  strike  the  hull.  It  should  be 
observed  that  the  vertical  .scale  is  different  from  that  of 
the  horizontal,  in  order  not  to  place  the  vessels  too  far 
apart  for  the  limited  size  of  the  plate ;  consequently,  the 
trajectory  shown  is  considerably  foreshortened. 

The  turret  represented  on  the  illustration,  in  which  the 
light  15-in.  shell-guns  are  mounted,  is  composed  of  wTought- 
iron  plates  of  great  thickness,  the  size  of  the  structure  being 
sufficient  to  accommodate  the  two  pieces,  suspended,  as  already 
stated,  by  pendulum-links  secured  under  the  I'oof.  A  massive 
central  shaft  of  wrought  iron  supjiorts  the  turret,  on  the  plan 
adopted  in  the  monitors.  The  vessel  designed  to  caii'v  the 
battery  is  a  mere  iron  hull,  eranimed  with  motive  power,  in 
order  to  ensure  high  speed.  The  midship  section  is  tri- 
angular and  tlie  bow  raking,  as  shown  by  the  illustration. 
The  overhanging  siiles  aud  deck  are  heavily  armored. 


CHAPTER   XLIIL 

SUBMARINE  WARFARE— THE  MOVABLE  TORPEDO. 
(SEE    PLATE   G3.) 


It  was  stated  as  a  general  proposition,  in  tte  preceding 
chapter,  that  a  heavy  body,  of  regular  form,  projected  late- 
rally through  the  air,  commences  to  fall  from  the  instant 
of  leaving  the  muzzle  of  the  gun,  describing  during  its  pro- 
gress a  parabolic  curve  considerably  foreshortened  owing  to 
atmospheric  resistance.  But  a  body  of  regular  form,  pro- 
jected under  the  surface  of  water  or  other  fluid,  in  a  hori- 
zontal or  inclined  direction,  will  move  in  a  straiglit  line, 
provided  its  sjiecific  gravity  be  equal  to  that  of  the  fluid. 
In  other  words,  a  heavy  body  moving  through  the  atmospliere 
is  under  the  influence  of  the  gravitating  force  of  the  earth  ; 
while  a  submerged  body,  the  weight  of  which  is  equal  to 
its  displacement,  is  not  affected  by  gravitation.  If  put  in 
motion  under  the  surface  of  a  quiescent  fluid  of  unlimited 
extent,  such  a  body  will  continue  to  move  in  a  straight  liue 


CHAP.  XLIII.  THE  MOVABLE    TOUrKDO.  541 

until  tlie  motive  energy  which  propels  it   liei-onies  less  than 
the  resisting  force  of  the  surrounding  niediiini. 

Starting  with  these  cardinal  propositions,  I  entered,  some 
thirty  years  ago,  on  the  task  of  solving  the  problem  of  sul)- 
marine  attack — viz.,  the  propelling  or  projecting  below  the 
surface  of  the  water  of  an  elongated  body  containing  explo- 
sive substances  to  be  ignited  when  reaching  some  point  under 
the  bottom  or  bilge  of  an  opponent's  vessel.  The  best  method 
of  carrying  out  the  idea  is  that  of  projecting  the  elongated 
body  by  means  of  a  tube  or  chamber  with  parallel  sides 
applied  near  the  bottom  of  the  aggressive  vessel.  Such  a 
method  I  proposed  to  the  Emperor  of  France  in  the  month 
of  September,  1854,  Jis  mentioned  in  Chap.  XXVIII. 

At  close  quartei-s  the  stated  plan  of  attack  will  unques- 
tionably be  found  very  effective — indeed,  infallible ;  but, 
unless  the  ojiponent's  vessel  can  be  approached  very  near, 
it  will  prove  abortive.  Oljviousl)^,  if  the  projectile  be  pushed 
out  in  any  direction  not  parallel  with  the  line  of  keel  while 
the  aggressive  vessel  is  in  motion,  a  side  resistance  will  be 
offered  by  the  stationary  water  of  the  sea,  \vhich  will  divert 
the  course  of  the  missile  the  instant  it  is  deprived  of  the 
guiding  power  of  the  tube  from  which  it  is  ejected.  Cur- 
rents will,  from  the  same  cause,  change  the  intended  course. 
It  need  scarcely  be  observed  that,  in  addition  to  the  difii- 
culty  of  controlling  the  direction  of  the  projectile,  tlie  force 
imparted  to  the  same,  whether  steana  or  compressed  air,  will 
be  insufficient  to  propel  it  to  any  considerable  distance.  In 
order  to   meet  these   sertous   practical    objections — viz.,  that 


542  THE  MOVABLE  TOEPEDO.  chap,  xliii. 

the  projectile  ('.iiiiint  l)e  propelled  far  enougli,  and  that  its 
course  cauuot  be  controlled — I  have  resorted  to  a  device  by 
which  any  desirable  amount  of  pi'opulsive  force  may  be  im- 
parted, irresjiective  of  the  distance  traversed,  and  by  which 
the  course  of  the  missile  is  undei'  perfect  control  dui-iiig  its 
progress  to  the  intended  point.  Persons  of  a  mechanical 
turn  of  mind  in  almost  every  country  have  for  a  long  time 
been  engaged  in  contriving  torpedoes  to  he  propelled  under 
water  by  independent  motive  power  of  various  kinds,  for 
the  purpose  of  blowing  up  vessels.  The  Austrian  torpedo, 
urged  through  the  water  by  means  of  compressed  air,  may 
be  classed  as  one  of  this  numeroiis  tribe,  the  reported  ter- 
]'il)le  nature  of  which  has  from  time  to  time  frightened  naval 
constructors,  and  amazed  some  uumechanical  sailors  who  have 
witnessed  the  trials,  and  found  that  the  mysterious  body 
actually  can  move  under  water.  Proper  investigation  of  the 
subject,  however,  exposes  imperfections  of  the  Austrian  tor- 
pedo which  i-ender  its  final  success  problematical. 

It  should  be  borne  in  mind  that  atmospheric  air  com- 
pressed, so  as  to  exert  a  pressure  of  300  lbs.  to  the  S(|.  in., 
weighs  nearly  2  ll)s.  to  the  cubic  ft.  Consecpiently,  the 
amount  of  motive  force  which  the  torpedo  is  capable  of 
containing  will  be  found  wholly  insulficient  for  its  effective 
jiropulsion  unless  an  imjiracticable  or,  at  any  rate,  dangei'ous 
pressure  be  employed,  accompanied  bj"  great  weight,  seiiousl}'' 
intei-fering  with  buoyancy,  while  the  want  of  means  for  direct- 
ing the  torjiedo  to  the  desired  point  presents  an  insupei'able 
objection.      As    before    stated,    I    have    contrived    a    torpedo 


iii.w.  XLiii.  TUE  MOVAHLE  'WHFEDO.  64^ 

that  limy  Ik-  [)ropflli'<I  witli  auy  rc.niisite  auiomit  of  force, 
invspoi-tive  of  dLstaiu-e,  the  course  of  which  is  uiuler  perfect 
control,  iiotwitli.staiuliug  currents,  and  which  may  be  directed 
with  i)erfect  certainty  to  an  object  in  motion.  In  contra- 
distinction to  the  term  [)rojcctiK',  ai)[.lied  to  tlie  structure  of 
1854,  which  was  i)roi)elled  alone  by  its  via  viva  on  leaving 
the  guiding-tube,  I  propose  to  apply  the  term  torpedo  to  tlie 
contrivance  now  to  be  considered. 

It  shoulil  be  observed  that  some  attempts  to  prtipel 
bodies  under  water  have  been  successful  as  regards  main- 
taining a  given  depth.  The  self-evident  device  of  ai)plyiiig 
a  tin  or  horizontal  rudder,  operated  by  a  2)iston  or  elastic 
bag  actuated  I)y  hydrostatic  i)ressure,  has  suggested  itself 
to  inventors.  It  will  be  readily  perceived  that  an  increase 
or  diminution  of  draught,  attended  as  it  is  with  a  corre- 
sponding variation  of  pressure,  may  be  made  subservient  in 
changing  the  inclination,  thereby  establishing  a  tendency  of 
the  horizontal  rudder  either  to  elevate  or  depress  the  torpedo 
during  its  forward  motion.  Thus,  by  a  proper  adjustment 
and  application  of  the  hydrostatic  pressure,  the  torpedo  may 
be  made  to  move  at  auy  desirable  depth  below  the  surface 
of  the  sea.  Nor  lias  any  difficulty  been  experienced  as 
regards  the  instrument  of  propulsion  in  the  experiments 
made  since  the  introduction  of  the  screw  pro]>eller.  But 
the  difficulty  of  procuring  the  requisite  amount  of  motive 
force  for  actuating  the  propeller,  and  the  aljsence  of  means 
for  directing  the  torpedo,  have  in  each  instance  defeated 
the  object  in  view. 


544  THE  MO  VABLE  TOliPEDO.  ■  chap,  xliii. 

Before  proceeding  to  consider  the  important  question  of 
gniding  the  torpedo,  I  will  uow  briefly  describe  my  method 
of  obtaining  the  required  power  for  actuating  the  propellers. 
A  reel,  of  suitable  diameter,  revolving  on  a  horizontal  axle, 
is  applied  near  the  chamber  from  which  the  torpedo  is 
ejected,  one  end  of  the  axle  being  supported  by  a  suitable 
bearing,  while  the  other  enters  an  air-vessel  through  a 
stuffing-box.  The  end  thus  inserted  in  the  air-vessel  is  per- 
foi'ated  longitudinally  for  a  short  distance,  and  provided  with 
an  ojjening  in  the  side  at  the  point  where  the  perforation 
terminates.  A  tubular  rope,  the  bore  of  which  is  about  one 
iucli  in  diameter,  composed  of  hemp  and  vulcanized  i-ubber, 
is  connected  with  this  opening,  and  then  coiled  around  the 
reel  a  certain  niimber  of  times,  and,  lastly,  connected  with 
the  rear  end  of  the  torpedo.  The  air-vessel  into  -which  the 
perforated  axle  of  the  reel  enters,  being  charged  with  com- 
pressed air  (by  means  of  force-pumps  worked  by  steam- 
power),  it  \vill  be  readily  understood  that  the  compressed 
air  will  pass  through  the  axle,  then  through  the  several 
coils  of  tubular  rope  wound  round  the  reel,  and  ultimately 
reach  the  rear  end  of  the  torpedo,  where  the  rope  is  attached 
to  the  engine  wliich  actuates  the  propellers.  Accordingly, 
the  propulsion  of  the  torpedo  may  be  regulated  by  simply 
o[)ening  or  closing  the  aperture  of  the  perforated  shaft  within 
the  air  vessel.  Tlie  rotation  of  the  reel,  consequent  on  the 
onward  movement  of  the  torpedo,  obviously  cannot  interrupt 
the  passage  of  the  compi-essed  air  through  the  coils  of  the 
tubular  rope;  hence  the  supply  of  motive  force  will  continue 


CHAP.  XLiii.  77/A'  MOVMU.E   ToniT.VO.  545 

iiMdiiiiinisIied  during  the  onward  niovona-nt.  Tlir  tulmlar 
rope  being  about  one  inch  diameter  in  the  bore,  it  will  be 
found  by  calculation  that  a  quantity  of  compressed  air,  suffi- 
cient to  develop  any  desirable  amount  of  power,  may  be 
transmitted  through  it  during  the  progress  of  the  torpedo, 
whether  far  oif  or  near  the  aggressive  vessel.  The  arrange- 
ment thus  described  being  sufficiently  simple  to  be  com- 
prehended without  entering  into  detail,  it  will  only  be 
necessary  to  state  that  the  tubular  rope,  after  leaving  the 
reel  under  the  deck,  is  made  to  descend  through  a  vertical 
tube  iuto  the  torpedo  chamljer,  iu  order  to  prevent  an 
entrance  of  water  at  the  point  where  the  rope  passes  out. 
Also,  that  tivo  propellers  are  employed,  revolving  in  opposite 
directions  round  a  common  centre — indispensable  to  prevent 
the  torpedo  itself  from  rotating  when  subjected  to  the 
powerful  torsion  produced  by  a  siiKjle  projieller  actuated 
by  the  motive  force  which  may  be  transmitted  through  a 
tuljular  rope  of  one-inch  bore. 

I  will  now  proceed  to  describe  my  method  of  guiding 
the  torpedo,  premising  that  the  external  casing  which  con- 
tains the  mechanism  and  explosive  compouud  is  heavier  at 
the  bottom  than  at  the  top,  in  order  to  preserve  a  vertical 
position,  and  that,  in  addition  to  the  horizontal  rudders  for 
regulating  the  immersion,  the  torpedo  is  provided  with  a 
vei-tical  balauce-rui^lder  for  directing  the  lateral  course.  The 
reel  having  a  mean  circumference  of  10  ft.,  it  will  be  seen 
that  the  tu1)ular  rope  need  only  l)e  coiled  rouii<l  it  100 
times  to  admit  of  attack   at  a   distance  of  l,0(in  ft.,  probably 


546  THE  MOVABLE  TORPEDO.  CHAP.  XLIII. 

far  enough,  since  tbe  position  of  tlie  aggressive  vessel  which 
carries  the  torpedo  may  be  changed  at  all  times  with  de- 
sirable rapidity. 

The  apparently  absurd  proposition  to  direct  and  change 
the  course  of  the  torpedo  at  will,  on  board  of  the  aggressive 
vessel,  without  external  aid,  is  solved  by  the  following  simple 
expedient:  A  small  elastic  bag,  connecting  the  tubular  rope 
Avith  the  induction-pipe  of  the  rotary  engine,  is  attached  to 
the  side  of  the  tiller  of  the  torpedo's  balance-i'udder.  As 
the  compressed  air  during  its  passage  to  the  motor  must 
pass  through  the  elastic  bag,  the  latter  will  expand  and 
contract  wdth  every  change  of  internal  pressure ;  and,  as 
such  change  will  depend  on  the  quantity  of  compressed  air 
admitted  into  the  tubular  rope,  the  expansion  and  contrac- 
tion of  the  bag  is  evidently  under  perfect  control.  No-\v, 
the  power  of  this  bag,  or  the  powder  of  a  loaded  piston  in 
an  open  cylinder,  to  resist  internal  pressure,  may  be  so  pro- 
portioned that  when  maximum  pressure  is  admitted  the 
swelling  of  the  bag,  or  the  motion  of  the  j)iston,  will  cause 
the  tiller  to  move  about  20  deg.  to  port;  and  Avhen  the 
pressure  is '  reduced  25  per  cent.,  the  accompanying  contrac- 
tion of  the  bag,  or  corresponding  motion  of  the  loaded  pis- 
ton in  the  open  cylinder,  will  move  the  tiller  20  deg.  to 
starboard.  Thus,  by  admitting  moi'e  or  less  compressed  air 
into  the  tubular  i-ope,  thereby  changing  the  dimensions  of 
the  bag  or  moving  the  piston  referred  to,  the  tiller  will  as- 
sume any  desirable  angle  within  20  deg.  on  either  side  of 
the  torpedo's  centi'e  line. 


CHAP.  XT.iii.  THE  MOVABLE   TOUrEDO.  5i7 

Accordingly,  the  direction  of  the  torpedo  will  be  as  com- 
pletely under  the  control  of  the  hand  which  admits  the  com- 
pressed air  to  the  tubular  rope  as  if  an  intelligent  directing 
power  resided  within  the  torpedo  itself.  Probably  no  greater 
mechanical  feat  than  this  can  be  instanced.  The  position  of 
the  torpedo  is  indicated  by  a  circular  disc,  four  inches  in 
diameter,  attached  to  the  upper  end  of  a  perpendicular  steel 
wire,  or  mast,  secured  to  the  top  of  the  torpedo.  The  said 
disc  is  painted  sea-green  on  the  forward  side  and  white  on 
the  opposite  side.  It  need  scarcely  be  observed  that  the 
explosion  of  the  torpedo  wnll  sever  the  connection  wath  the 
tubular  rope,  w-hich  thus  may  be  hauled  in  by  turning  the 
reel.  Should  the  intended  object  not  be  reached,  the  admis- 
sion of  compressed  air  to  the  tubular  rope  Avill  be  shut  off, 
and  the  torpedo  hauled  in,  or  sent  out  on  a  new  errand. 

The  scope  of  the  device  thus  described  is,  of  course,  more 
limited  than  the  scope  of  the  method  illustrated  on  PI.  62 ; 
yet,  had  the  Italians  possessed  it,  the  result  at  Lissa  would 
unquestionably  have  been  revereed.  No  harbor  can  be  entered 
which  is  protected  by  it ;  nor  would  any  amount  of  vigilance 
save  vessels  from  destruction  if  approaching  an  enemy's  coast 
defended  by  it. 

With  reference  to  the  reel  on  which  the  tubular  lope  is 
coiled,  it  will  be  well  to  mention  that  it  may  be  applied 
within  the  toi'pedo  itself;  in  which  case  the  tubular  rope, 
instead  of  being  (otved,  will  be  paid  out  during  the  onward 
motion  towards  the  object  intended  to  be  struck. 

The  illustrations  on  PI.  63,  Figs.  1   and  2,  represent  top 


548  THE  MOVABLE  TOBPEDO.  chap,  xliii. 

vie^\"  and  side  elevation  of  the  actuating  steam-engine,  air- 
compressing  pump,  air-vessel,  and  reel ;  while  Figs.  3  and 
4  show  the  side  elevation  and  top  view  of  the  torpedo.  It 
may  be  briefly  mentioned  that  the  torpedo  thus  represented, 
after  having  been  tested  during  a  series  of  ti'ials  in  open 
\vater,  has  been  purchased  by  the  Navy  Department  at  Wash- 
ington. Negotiations  are  now  pending  for  the  purchase  of 
the  invention  Ijy  the  United  States  Government,  on  conditions 
of  secrecy,  as  in  the  case  of  the  Austrian  torpedo «;  hence 
detailed  information  respecting  the  internal  mechanism  can- 
not be  presented  in  this  work. 


CHAPTER   XLTY. 

TRANSMISSJOX    OF   MIX'IIAXKAL    I'uWER   BY    COM- 
PRESSED  AIU. 

(SEE    PLATKS    04    AM)    05.) 


Professor  Barijard,  in  his  admirable  report  of  the  Paris 
Universal  Exposition,  observes  "  tliat,  next  in  impoitance  to 
the  creation  of  a  new  motive  power,  may  lie  jilaced  any 
material  improvement  in  tlic  methods  of  makiiiir  available 
the  powers  which  we  have.  Natnre  often  fnrnishes  ns  with 
such  powers  in  abundance  in  situations  whei-e  they  cannot 
be  conveniently  converted  to  use.  The  positions  of  waterfalls 
are  determined  by  geographical  accidents.  These  do  not 
always  conspire  with  the  causes  which  promote  the  growth 
of  to\\Tis  and  development  of  industries.  If  it  were  jiossible 
to  transfer  the  imnn-nse  forces  which  are  thus  unprotitablv 
ex])ending  themselves  to  points  where  there  are  hands  to 
direct  them,  and  materials  on  which  to  employ  them,  thev 
might  be  productive  of  incalculal)le  wealth,  and  of  immea- 
surable benefit  to  mankind." 


650  TBANSMIS8I0N  OF  POWER.  chap.  xliv. 

Tlie  foregoing  views,  so  well  expressed,  are  quite  cor- 
rect ;  but  there  is  another  power  running  to  waste  which 
the  engineer,  ere  long,  will  be  called  upon  to  utilize — viz., 
the  230wer  of  the  tides.  Already  a  prominent  association 
has  been  formed  in  France  for  erecting  tidal  motors  on  a 
very  large  scale.  Thus,  while  engineering  skill  has  nearly 
exhausted  itself  in  endeavors  to  imjM'Ove  the  steam-engine, 
a  new  field  opens,  boundless  in  extent,  which  will  demand 
far  greater  abilities  than  those  called  for  within  the  narrow 
bounds  hitherto  limiting  the  energies  of  the  mechanical  engi- 
neer. The  grand  scheme  of  utilizing  the  natural  forces  now 
running  to  waste  divides  itself  into  two  distinct  branches  : 
1st.  The  requisite  mechanism  for  receiving  the  force  exerted 
by  nature.  2d.  The  means  for  transmitting  that  force  to 
desirable  localities.  It  is  the  latter  branch  which  I  propose 
to  discuss.  But,  before  entering  on  the  subject,  it  will  be 
proper  to  point  out  that  it  is  not  the  natural  forces  alone 
which  the  engineer  is  called  upon  to  devise  means  for  trans- 
mitting. Indeed,  with  our  present  abundant  supi:)ly  of  coal, 
the  transmission  of  force  developed  by  steam  will  be  most  fre- 
quently called  for;  since  the  steam-engine,  however  j^ortable 
in  its  character,  cannot  be  applied  in  all  places  where  power 
is  required.  The  experience  of  late  years  has  shown  that 
the  substitution  of  mechanical  power  for  manual  labor  in 
driving  tunnels  and  for  mining  operations  has  reduced  the 
cost  and  greatly  increased  the  amount  of  work  done  in  a 
given  time.  But  the  presence  of  steam  in  tunnels  and  in 
the  galleries  of  mines    is  wholly  inadmissible;    hence    small 


C11AI-.  xi.iv.  TlUXiiMli^SIOy  OF  I'OWEB.  55] 

motive  engines,  operated  hy  compressed  air,  liave  been  intro- 
duced for  operating  tlie  luck-drills  and.  otliei-  cutting  tools. 
Not  oidy  La;s  the  work  by  these  means  beeh.  greatly  acce- 
lerated, but  the  escape  of  the  exliaust  air  from  tlie  motors 
has  in  a  material  degree  tended  to  purify  the  atmosphere 
within  the  mines,  rendering  the  work  healthful  wliich  for- 
merly proved  destructive  to  the  miners. 

The  first  question  which  presents  itself  iu  treating  of  the 
transmission  of  force  by  compressed  air  is  the  size  of  the  tube 
necessary  to  convey  a  certain  amount  of  energy  in  a  given 
inuQ—presmre  and  velocity  being  the  elements  which  deter- 
mine the  question.  Fortunately,  we  are  not  without  prac- 
tical data  on  the  subject,  the  engineers  of  the  :Mont  Cenis 
tunnel  having,  some  time  ago,  thoroughly  investigated  it. 
The  result  of  their  labors  has  been  recorded  iu  the  Report 
of  the  United  States  Commissionei-s  at  the  Paris  Universal 
Exposition  of  1S67.  The  Commissioners  state  that,  at  the 
date  of  the  report  on  the  pi-ogress  of  the  work  in  the  tunnel 
during  the  year  1863,  the  operation  was  carried  on  at  a  dis- 
tance of  nearly  two  thousand  metres  from  the  reservoii-s  of 
compressed  air,  and  that  nine  borers  were  in  operation  witli 
a  force  of  two  and  a  half  horse-power  each.  The  tube  con- 
veying the  air  w:vs  very  nearly  eight  inches  in  diameter,  the 
air  being  under  a  pressure  of  six  atmospheres,  and  its  ve- 
locity in  the  tube  three  feet  per  second.  The  transmission 
of  the  power  under  these  very  favorable  conditions  was  at- 
tended with  no  sensible  loss,  the  pi-essure  not  being  percep- 
tibly less   at    the   working  extremity  of   the  tube   when  all 


553  TEANSMIlSi<10X  OF  FOWEB.  chap.  xliv. 

the  perforations  were  in  operation  than  when  the  machinery 
■was  entirely  at  rest. 

The  Keport  of  the  Commissioners  furnishes  a  very  full 
account  of  the  result  of  the  exj^eriments  conducted  at  Cor- 
sica, in  1837,  by  order  of  the  Italian  Government,  on  the 
resistance  of  tubes  to  the  ilow  of  air  through  them.  These 
experiments  were  made  previously  to  tlie  commencement  of 
the  work  on  the  tunnel,  the  employment  of  compressed  atmo- 
spheric air  as  a  motive  power  to  actuate  the  boring  a2:)paratus 
being  at  the  time  considered  a  doubtful  expedient.  The  Re- 
port states  that  it  was  the  aim  of  the  investigation  not  only 
to  ascertain  the  absolute  loss  of  force  attending  the  trans- 
mission of  air  through  tubes  of  certain  dimensions  at  certain 
velocities,  but  also  to  determine  what  are  the  laws  whicli 
govern  the  resistance  wlien  the  velocities  of  the  air  and  the 
diameter  of  the  tube  are  varied.  The  following  conclusions 
Mere  deduced  from  the  experiments :  1.  The  resistance  is 
directly  as  the  length  of  the  tube.  2.  It  is  directly  as  the 
square  of  the  velocity  of  flow.  3.  It  is  inversely  as  the 
diameter  of  the  tube. 

The  fact  before  adverted  to — that  in  the  actual  Avorking 
of  the  machines  in  the  tunnel  no  perceptible  loss  of  power 
was  experienced  at  a  distance  of  two  thousand  metres  from 
the  reservoirs — must  be  attributed  to  the  want  of  delicacy 
of  the  manometer  or  pressure-gauge  employed.  Although 
insignificant  at  moderate  distances  and  low  velocities,  the 
experiments  at  Corsica  proved  that  the  loss  becomes  serious 
when   the   velocity    and    distance    are    considerably  increased 


CHAP.  XLIV.  TBANSMISSION  OF  FOWER.  653 

since,  agreeably  to  the  law  before  cited,  the  resistance  varies 
as  the  square  of  the  velocity.  Consequently,  when  the  velo- 
city is  six  times  greater  than  the  moderate  rate  of  six  feet, 
or  thirty-six  feet  per  second,  the  resistance  will  be  thirty-six 
times  greater,  the  power  developed  increasing  in  the  ratio 
of  the  volume  of  air  delivered — viz.,  six  times.  It  will  be 
perceived,  therefore,  that  while  the  length  and  diameter  of 
a  tube  remain  unaltered,  and  while  the  absolute  resistance 
opposed  to  the  floAV  of  a  current  of  air  through  it  varies  as 
the  square  of  the  velocity,  the  relative  resistance  is  only  as 
the  simple  velocity.  It  follows  from  the  foregoing  facts 
that  the  power  of  compressed  air  varies  as  the  product  of 
its  pressure  and  its  volume;  hence,  when  the  pressure  is 
constant,  as  the  volume  simply.  But  the  volume  delivered 
varies  as  the  velocity  multiplied  by  the  square  of  the  dia- 
meter of  the  tube.  Now,  as  the  resistance  is  inversely  as 
the  diameter,  and  the  volume  directly  as  the  square  of  the 
diameter  when  the  velocity  remains  constant,  it  follows  also 
that  under  a  given  pressure  and  velocity  the  relative  resist- 
ance (namely,  the  resistance  divided  by  the  power)  will  vary 
invei-sely  as  the  cube  of  the  diameter.  Obviously,  therefore, 
by  enlarging  the  diameter  of  the  tube,  we  may  increase  the 
power  transmitted,  and  at  the  same  time  diminish  both  the 
absolute  and  relative  resistance.  In  conclusion,  I  strongly 
recommend  engineei-s  who  may  be  called  upon  to  transmit 
mechanical  power  by  compressed  air  not  to  aim  at  economy 
by  employing  tubes  of  small  diameter. 

Having  thus  disposed  of  the  fii-st  branch  of  the  subject 


554  TBANSMISSION  OF  POWEB.  chap.  xliv. 

under  consideration,  let  us  now  consider  the  meclianism 
needed  to  compress  the  air  to  be  transmitted.  At  first 
sight  the  solution  of  the  problem  appears  to  be  very  simple, 
but  due  reflection  at  once  suggests  to  the  practical  mind 
numerous  difliculties.  Considerations  of  weight,  space,  and 
first  cost,  of  course,  demand  the  adoption  of  a  double-acting 
compressiug-cylinder ;  hence  the  practicability  of  employing 
double  action  is  the  very  first  question  that  pi'esents  itself. 
Now,  in  double-acting  cylinders  both  ends  must  be  closed, 
consequently  lubrication  of  the  compressing  piston  must  be 
effected  from  without.  Supposing  that  means  for  effecting 
such  lubrication  have  been  devised  (by  no  means  easy),  will 
the  packing  of  the  piston  be  preserved  and  abrasion  pre- 
vented? In  answering  this  question,  we  must  bear  in  mind 
that  even  at  moderate  pressure  the  compression  of  the  air 
generates  a  degree  of  heat  which  precludes  the  employment 
of  oil,  as  it  quickly  dries  up  and  ultimately  burns.  Water, 
if  continually  replenished,  so  as  to  make  good  the  loss  caused 
by  the  formation  of  steam,  may  answer  for  a  short  time.  The 
dust  drawn  into  the  cylinder  from  the  surrounding  atmo- 
sphere will,  however,  mix  ^\-ith  the  ^vater,  and  soon  form  a 
paste,  resembling  mud,  on  the  piston,  productive  of  friction 
and  abrasion  of  the  cylinder  incompatible  with  the  functions 
of  a  piston.  The  objectionable  plan  of  compressing  air  by 
rising  and  falling  columns  of  water  I  do  not  propose  to 
discuss  in  this  place. 

The  illustrations  on  Plate  64  represent  a  perspective  view, 
while  Plate   65   shows  a  longitudinal  section    of   a    machine 


CHAP.  XLIT.  TIiAN8MTS8I0X  OF  POWER.  555 

for  compressing  air,  in  which  the  difficulties  before  referred 
to  have  been  effectually  overcome;  the  leading  features  beino- 
that  the  compressing  cylindei-s,  open  at  the  top,  are  immersed 
in  a  cistern  through  wliich  a  continuous  circulation  is  kept 
up  by  a  current  of  water  Avliicli  (lows  over  the  corapressino' 
pistons  before  entering  the  cistern.  A  glance  at  the  sec- 
tional di-awing  on  Plate  65  will  give  a  clear  idea  of  the 
nature  of  the  device  and  the  mode  of  operation,  which  may 
be  thus  briefly  described  :  A  small  pipe  communicating  with 
a  reservoir  or  other  supply  of  water  is  applied  behind  the 
machine,  proWded  with  a  branch  for  each  compressing 
cylinder.  These  branch-pipes  are  bent  downwards  vertically 
in  such  a  manner  that  a  stream  of  water  flowing  throufli 
each  will  fall  on  the  top  of  the  comj)ressing-piston,  near 
its  circumference.  The  conipressing-cylinders,  as  already 
stated,  are  suspended  within  a  water-cistern,  and  supported 
by  their  upper  flanges,  which  rest  on  the  toji  of  the  cistern. 
Referring  to  the  perspective  view  of  the  machine,  shown 
on  Plate  64,  it  will  be  seen  that  the  water-cistern  forms  a 
pedestal  supporting  the  side  frames  on  which  the  pillow- 
blocks  of  the  crank-journal  rest.  It  will  also  be  seen  that 
the  side  frames  form  slides  which  guide  the  cross-head  of 
the  piston-rods.  A  band-wheel,  provided  with  a  very  heavy 
rim,  to  be  driven  by  steam  or  other  motive  power, 
is  attached  to  the  crank-shaft  between  the  pillow-l)]ock3 
formed  at  the  top  of  the  side  frames.  It  scarcely  needs  ex- 
planation that  the  object  of  making  the  rim  of  the  band- 
wheel  veiy  heavy  is  tliat  of  ecpializiug  the  irregular  resistance 


556  TRANSMISSION  OF  POWER.  chap.  xliv. 

offered  by  the  compressing-pistons.  The  inlet-valves  which 
supply  the  atmospheric  air  to  be  compressed  are  inserted  in 
the  pistons,  while  the  outlet-valves  are  placed  at  the  bottom 
of  the  cylinder,  the  valve-chambers  of  the  latter  communi- 
cating directly  with  an  air-conductor  which  leads  to  an  ordi- 
nary air-reservoir.  Referring  again  to  the  sectional  repre- 
sentation of  the  machine,  it  will  be  seen  that  the  sides  of 
the  compressing-cylinder  are  perforated  near  the  top,  the 
position  of  these  perforations  being  such  that  when  the  pis- 
ton reaches  the  full  up-stroke  its  upper  face  will  not  quite 
reach  the  under  side  of  the  perforations.  It  will  be  readily 
understood  that  b)^  this  arrangement  a  certain  body  of  water 
will  always  remain  on  the  top  of  the  piston,  while  at  the 
same  time  the  perforations  effectually  prevent  an  overflow 
within  the  cylinder.  The  connecting-rod  is  very  short  com- 
pared with  the  length  of  throw  of  the  crank ;  hence  the 
piston  will  remain  for  a  considerable  interval  of  time  near 
the  top  of  the  cylinder,  during  which  time  the  necessary 
discharge  of  the  water  lodged  on  the  top  of  the  piston  takes 
place.  To  prevent  undue  accumulation  of  water  in  the  cis- 
tern, an  overflow-pipe  is  introduced  at  the  side,  as  shown  in 
the  sectional  illustration.  It  should  be  particularly  noticed 
that  the  air,  \vhile  undergoing  compression  in  the  cylinder, 
is  completely  surrounded  by  metallic  surfaces  cooled  by  the 
circulating  water.  But  this  is  not  all.  During  the  recipro- 
cating action  of  the  piston,  the  body  of  water  lodged  on  its 
top  washes  the  inside  of  the  cylinder  both  during  the  upward 
and   downward    movement.     Now,    the    speed   of    the    piston 


CHAP.  XLIV.  TRANSMISSIOX  OF  POWER.  557 

is  fully  one  luimlred  and  fifty  feet  per  minute;  hence  an 
internal  refrigeration  is  established  far  more  efficient  than 
the  external  circulation.  The  metal  composing  the  cylinder, 
it  will  thus  be  seen,  is  actually  cooled  on  both  sides,  a  very 
remarkable  and  almost  paradoxical  achievement.  Again,  it 
will  be  perceived  that  the  circulating  cold  water  continually 
washes  the  top  of  the  piston  before  entering  the  cistern. 
Accordingly,  the  entire  quantity  of  water  required  for  cooling 
during  the  compression  passes  over  the  piston  at  the  initial 
low  temperature,  thereby  subjecting  the  part  of  the  machine 
that  most  needs  cooling  to  the  greatest  amount  of  refrigera- 
tion. As  regards  lubrication,  it  is  self-evident  that  no  con- 
ceivable plan  can  be  more  efficient  than  that  of  actually 
washing  the  inside  of  the  cylinder  with  the  lubricating 
medium,  both  during  the  up  and  down  movement  of  the 
piston. 

Regarding  the  utility  of  cooling  the  compressed  air,  it 
needs  no  demonstration  to  show  that  refrigeration  after  the 
air  has  left  the  compressing-cylinder,  recommended  by  some 
engineer,  is  not  only  useless,  but  tends  to  reduce  the  effi- 
ciency of  the  compressed  air  as  a  motive  agent.  Obviously, 
if  the  air  during  its  transmission  from  the  compressor  to 
the  motor  intended  to  be  actuated  loses  in  temperature,  it 
also  loses  in  bulk.  On  the  other  hand,  refrigeration  witltin 
(lie  cylinder  during  the  down-stroke  is  useful,  as  it  tends  to 
check  the  swelling  of  the  volume  of  air  under  the  piston 
caused  by  the  heat  generated  by  compression,  consequently 
diminishing  the  necessary  motive  power. 


CHAPTER   XLY. 

SUN   POWER— THE   SOLAR   ENGINE. 
(SEE    PLATES    GO    AND    67.) 


The  illustration  on  Plate  66  derives  its  cliief  interest 
from  the  fact  that  it  represents  the  first  motor  actuated  by 
the  direct  agency  of  the  sun's  radiant  heat.  It  was  con- 
structed at  New  York,  IS 70,  and  intended  as  a  present  to 
the  French  Academy  of  Sciences.  Apart  from  being  a  motor, 
this  engine  was  designed  to  operate  as  a  meter  for  register- 
ing the  volume  of  steam  generated  by  the  concentrated  heat 
of  a  pencil  of  solar  rays  of  a  given  section.  Regarded  as 
a  steam-meter,  it  proved  important,  as  it  verified  the  results 
of  previous  experiments  and  previous  calculations,  based  on 
the  number  of  thermal  units  developed  by  the  evaporation 
of  a  certain  weight  of  ^vater  in  a  given  time.  Engineers  will 
not  fail  to  notice  the  unusual  proportions  of  the  working 
parts,  nor  will  they  fail  to  appreciate  the  object  in  view, 
that    of   reducing  the  friction  to   a  minimum — an   iudispens- 

658 


CHAP.  XLV.  SUX  POWER— TUE  SOLAR  E.XGIXE.  559 

able  coiulitiou  in  a  meter.  Tlie  entire  nicobiinisni  being 
shown  with  perfect  distinctness  in  the  pei-spective  view  of 
the  engine  on  the  plate  referred  to,  it  is  only  necessuiy  to 
mention  that  the  square  pedestal  which  suppoi-ts  the  steam- 
cylinder  (4J  ins.  in  diameter),  the  beam-centre,  and  the 
crank-shaft,  conceals  a  surface-condenser. 

Under  a  clear  sun  the  engine  performed  its  functions 
with  pei-fect  uniformity,  at  a  velocity  of  240  revolutions  per 
minute.  It  consumed,  at  the  stated  rate,  only  part  of  the 
steam  furnished  by  a  solar  steam-generator,  temporarily  em- 
ployed, belonging  to  an  engine  of  greater  dimensions  then 
in  the  course  of  construction.  With  reference  to  ascertaining 
correctly  the  amount  of  mechanical  po\ver  developed  by  the 
concentrated  radiant  heat  applied  to  thi.s  engine,  experts 
need  scarcely  be  reminded  that,  by  dispensing  with  a  vacuum, 
the  atmospheric  resistance  and  back  pressure  exerted  against 
the  piston  furnish  elements  for  measuring,  with  critical 
nicety,  the  dynamic  foi-ce  transmitted  by  pencils  of  solar 
rays  of  definite  sections. 

Drawings  and  descriptions  of  the  mechanism  by  which 
the  sun's  radiant  heat  has  been  concentrated  in  my  experi- 
mental engines  will  not  be  presented  in  this  work,  nor  wnll 
the  form  of  the  steam-generator  which  receives  the  concen- 
trated heat  be  delineated  or  described.  Experienced  pro- 
fessional men  will  appreciate  the  motive — viz.,  that  of  pre- 
venting enterprising  persons  from  procuring  patents  for 
mod  if  cation. 9.  With  reference  to  the  course  thus  adopted, 
it  will  be  pioper  to  mention  that  I  have  in  several  instances, 


560  SUN  PO WEB— THE  SOLAR  ENGINE.  chap.  xlv. 

notably  in  the  case  of  tlie  screw-propeller  and  tlie  caloric 
engine,  been  prevented  from  perfecting  my  invention  in  con- 
seqnence  of  conflicting  privileges  having  in  the  meantime 
been  granted  to  otliers. 

Regarding  the  solar  engine,  it  may  be  well  to  state  that 
I  shall  not  apply  for  any  patent  rights,  excepting  for  the 
purpose  of  protecting  the  community,  and  that  it  is  my 
intention  to  devote  sufficient  time  and  means  to  ensure  its 
completion.  Hence  my  anxiety  to  guard  against  legal  ob- 
structions being  interposed  before  perfection  of  detail  shall 
have  been  measurably  attained.  In  the  meantime,  let  us 
hope  that  no  exclusive  privilege  will  be  granted  tending  to 
throw  obstacles  in  the  way  of  an  unrestricted  manufacture 
and  introduction  of  the  solar  engine  in  countries  where  a 
continuously  clear  sky  warrants  its  adoption,  especially  in 
Upper  Egypt  and  on  the  coast  of  Peru. 

The  experiments  instituted  show  that  the  mechanism 
■\vhich  I  have  adopted  for  concentrating  the  sun's  radiant 
heat  abstracts,  on  an  average,  during  nine  hours  a  day,  for 
all  latitudes  between  the  equator  and  45  deg.,  fully  3.5  units 
of  heat  per  minute  for  each  square  foot  of  area  presented 
perpendicularly  to  the  sun's  rays.  A  unit  of  heat  being 
equivalent  to  772  foot-pounds,  it  will  be  perceived  that, 
theoretically,  a  dynamic  energy  of  2,702  foot-pounds  is 
transmitted  by  the  radiant  heat,  per  minute,  for  each  square 
foot;  hence,  270,200  foot-pounds  for  an  area  of  10  feet 
square.  If  we  divide  this  sum  by  the  adopted  standard, 
33,000,   we   ascertain    that    100    square    feet   of    surface   ex- 


CHAP.  XLV.  sry  POWEli~TUE  HOLAU'ESGINE.  otil 

lH)sed  to  the  solar  rays  develop  coiitiuuously  8.2  horse- 
power during  nine  houi-s  a  day,  within  the  limits  of  lati- 
tude before  iiientioued.  But  eugiueei-s  are  well  aware  that 
the  whole  dynamic  energy  of  heat  cannot  be  utilized  in 
piactioe  l)y  any  engine  or  mechanical  combination  what- 
ever, nor  at  all  approached  ;  hence  I  have  assumed,  in  order 
not  to  oven-ate  the  capability  of  the  new  system,  that  a 
solar  engine  of  one  horse-power  demands  the  concentration  of 
solar  heat  from  an  area  of  10  feet  square.  On  this  basis, 
I  will  show  presently  that  those  regions  of  the  earth  which 
suifer  from  an  excess  of  solar  heat  will  ultimately  derive 
benefits  resulting  from  an  unlimited  command  of  motive 
power  which  will,  to  a  great  extent,  compensate  for  disad- 
vantages hitherto  supposed  not  to  be  counterbalanced  Ijy 
any  good.  But  before  estimating  the  magnitude  of  me- 
chanical poAver  wliich  we  may  produce  by  availing  our- 
selves of  the  fuel  contained  in  that  great  storehouse  from 
whence  it  may  be  obtained  fi-ee  of  cost  and  transportation, 
let  us  consider  the  leading  feature  of  the  device  resorted 
to,  especially  that  by  which  I  have  succeeded  in  augment- 
ing the  comparatively  low  temperature  developed  by  direct 
solar  radiation  sufliciently  for  the  production  of  useful  work. 
The  solar  engine,  when  steam  is  employed  as  the  medium 
for  transmitting  the  radiant  energy,  is  comjiosed  of  tlii-ee 
distinct  parts — the  engine,  the  steam-generatoi-,  and  the  me- 
chanism by  means  of  which  the  inadequate  energy  of  the 
sun's  rays  adverted  to  is  increased  to  such  a  degree  that 
the  resulting  temperature  will  exceed  that  corresponding  with 


563  SUN  FOWEll-THE  SOLAS  ENGINE.  chap.  xlv. 

the  steam-pressure  necessary  in  an  efficient  engine.  The 
motor  itself,  wLeu  tlie  acting  medium  under  consideration  is 
employed,  resembles  in  all  essential  points  a  modern  steam- 
engine,  utilizing  to  tlie  fullest  extent  tlie  mechanical  energy 
of  the  steam  admitted  to  the  working-c}linder.  But  when 
atmospheric  air  is  employed  as  the  medium  for  transmitting 
the  solar  energy  to  the  motor,  an  entirely  different  conihiua- 
tion  of  mechanism  is  called  for,  as  will  l^e  seen  hereafter. 
Regarding  the  steam-generator,  it  will  he  superfluous  to  point 
out  the  advantages  resulting  from  its  not  being  exposed  to 
the  action  of  fire  or  soot ;  hence  that  it  can  only  suffer  from 
the  slow  action  of  ordinary  oxidation.  As  the  motor  itself 
resembles  a  steam-engine,  we  have  of  course  merely  to  con- 
sider the  nature  of  the  mechanism  by  means  of  which  the 
solar  heat  is  concentrated  and  the  temperature  raised  above 
that  of  the  water  in  the  steam-generator.  Regarding  this 
mechanism — viz.,  the  concentration  apparcUus — it  has  been 
asked,  Is  it  costly  ?  Is  it  heavy  and  bulky,  so  as  to  render 
transportation  difficult?  And,  finally,  the  question  has  fre- 
c^uently  been  put,  Is  it  liable  to  derangement  and  expensive 
to  keep  in  order?  The  cost  is  moderate.  The  weight  is 
small ;  indeed,  lightness  is  the  most  notable  peculiarity  of 
the  concentration  apparatus.  As  to  bulk,  it  may  be  observed 
that  this  apjjaratus  is  composed  of  small  parts  readily  put 
together.  With  reference  to  durability,  the  fact  need  only 
be  pointed  out  that  certain  metals,  however  thin,  if  kept 
dry,  may  be  exposed  to  the  sun's  rays  during  an  indefinite 
length    of    time    without    appreciable    deterioration ;    hence, 


OIIAI-.  XLV.  SUX  rOWER—TllE  SOLAE  EXGTXE.  503 

unlike  the  funi;u"L's  of  steam-boilers,  which  soon  Ijecouie 
uuserviceable,  the  couceutratioii  apparatus,  as  it  consists  of 
thiu  metallic  plates,  composed  of  durable  materials,  cannot 
be  damaged  by  the  mere  action  of  the  sun's  rays.  Another 
question  has  been  asked,  Whether  the  solar  engine  will 
answer  as  well  on  a  large  as  it  does  on  a  small  scale  i  The 
following  reply  disposes  of  this  pregnant  query :  It  is  not 
necessary,  nor  intended,  to  enlarge  considerably  the  size  of 
the  apparatus  by  means  of  which  the  comparatively  feeble 
intensity  of  the  sun's  rays  has  been  successfully  concentrated, 
and  the  temperature  sufficiently  elevated  to  generate  steam 
for  actuating  the  solar  engine.  The  maximum  size  adopted 
has  been  adequate  to  utilize  the  radiant  heat  of  a  pencil  of 
rays  (^sunbeam)  of  35  square  feet  section.  The  employment 
of  an  increased  number  of  such  structures  will,  therefore,  in 
most  cases  be  resorted  to  when  greater  power  is  wanted,  as 
we  increase  the  lumiber  of  hands  when  we  desire  to  perform 
an  additional  amount  of  work.  The  motor  itself — viz.,  the 
steam-cylinder  and  the  working  parts — will  obviously  be  pro- 
portioned, as  at  present,  in  accordance  with  the  pressure  of 
steam  employed  and  the  work  to  be  done. 

It  should  be  clearly  understood  that  I  do  not  recommend 
the  erection  of  solar  engines  in  places  where  there  is  not 
steady  sunshine,  until  proper  means  shall  have  been  devised 
for  storing  up  the  radiant  energy  in  such  a  manner  that 
regular  power  may  be  obtained  from  irregular  solar  radia- 
tion. E.xperienced  engineers  need  not  be  toltl  that  formidal^le 
difficulties  present  themselves  in  stoi-ing  up  mechanical  energy 


564  SUN  POWEE-THE  SOLAS  ENGINE.  CHAP.  XLV. 

of  auy  kind ;  yet  when  coal  can  no  longer  be  obtained, 
necessity,  ingenuity,  and  increased  experience  will  find  means 
of  overcoming  obstacles  wliicli  now  appear  insurmountable. 

Before  considering  further  the  nature  and  capabilities  of 
my  solar  engine,  it  will  be  proper  to  notice  the  result  of 
the  labors  of  Professor  Mouchot  of  Tours,  formerly  of  the 
Lycee  of  Alengon,  who  claims  to  have  anticipated  me  in 
employing  solar  heat  for  the  production  of  motive  power. 
Mouchot  bases  his  claim  on  some  experiments,  made  in 
1866,  intended  to  show  that  by  the  accumulation  of  heat 
which  takes  place  when  a  blackened  surface  is  surrounded 
by  glass  bells,  steam  may  be  generated  for  actuating 
machinery.  Sir  John  Herschel,  it  is  well  known,  ela- 
borated the  old  idea  of  concentrating  solar  radiation,  and 
conducted  a  series  of  experiments  at  Cape  Town,  in  1838, 
showing  that  not  only  was  it  possible  to  produce  boiling 
heat  by  accumulating  solar  heat  as  described,  but  he  suc- 
ceeded in  elevating  the  temperature  sufficiently  foi'  roasting 
meat.  Some  time  previous  to  1870,  Mouchot  made  a  small 
model  engine,  a  mere  toy,  actuated  by  steam  generated  on 
the  plan  of  accumulation  by  glass  bells ;  but  finding  the 
heat  insufficient,  he  added  a  polished  metallic  reflector. 
The  increase  of  temperature  resulting  from  this  expedient 
rendered  his  steam-generator  more  effective,  and  it  was 
found  that  under  favorable  circumstances  sufficient  steam 
could  be  produced  to  actuate  his  small  model.  The  Con- 
seil-Gen^ral  of  Indre-et-Loire  having  subsequently  provided 
Professor  Mouchot  with  necessary  means,  he  put  u^t  a  steam- 


SUN  POWEK-THE  SOLAR  ENGLSE. 


505 


geuerator  at  Tours  in  1S72,  wliich  he  deems  a  pei-fect  inaebiiie, 
its  action  beiug  based  on  the  results  of  his  previous  experi- 
ments. The  accompanying  diagram,  Fig.  1,  represents  a  ver- 
tical section  of  the  said  steam-generator,  thus  described  by 
]\r.  L.  Simonin  in  lievue  des  Deux  Mondes  : 

"The   traveller  who   visits  the  libi-ary   of  Tours  sees    in 
the  court-yard  in  front  a  strange-looking  a})paratus.     lma"-in«' 


an  immense  truncated  cone,  a  mammoth  lamp-shade,  with 
its  concavity  directed  skyward.  This  apparatus  is  of  copper, 
coated  on  the  inside  \\\W\  veiy  thin  silver-leaf.  On  the 
small  ba.se  of  the  truncated  cone  rests  a  copper  cylinder, 
blackened  on  the  outside,  its  vertical  axis  being  identical 
with  that  of  the  cone.  This  cylindei',  surrounded  as  it  were 
by  a  great  collar,  terminates  above  in  a  hemispherical  cap, 
so  that  it  looks  like  an  enormous  thimble,  and  is  covered 
with  a  bell-glass  of  the  same  shape. 

"This  curious  apparatus  is  nothing  else  but  a  solar  receiver, 


5G6  SUN  rOWEB—TUE  SOLAll  ENGINE.  chap.  xlv. 

or,  ill  <,)tliei'  words,  a  boiler,  in  wliicli  water  is  made  to  boil 
by  the  beat-rays  of  tlie  suo.  This  steam-generator  is  designed 
to  raise  water  to  the  boiling  point  and  beyond,  by  means 
of  the  solar  rays,  ^vhich  are  thi'o^vn  upon  the  cylinder  by 
the  silvered  inner  surface  of  the  conical  reflector.  The  boiler 
receives  water  up  to  two-thirds  of  its  capacity  through  a 
feed-pipe.  A  glass  tube  and  a  steam-gauge  communicating 
with  the  inside  of  the  generator,  and  attached  to  the  outside 
of  the  reflector,  indicate  both  the  level  of  the  water  and 
the  pressure  of  the  steam.  Finally,  there  is  a  safety-valve 
to  let  off  the  steam  when  the  pressure  is  greater  than  desired. 
Thus  the  engine  offers  all  desirable  safety,  and  may  be  pro- 
vided with  all  the  accessories  of  a  steam-l)oiler. 

"  The  reflector,  which  is  the  main  portion  of  the  generator, 
has  a  diameter  of  2.60  metres  at  its  large,  and  one  metre 
at  its  small,  base,  and  is  eighty  centimetres  in  height,  giving 
four  square  metres  of  reflecting  surface,  or  of  insolation.  The 
interior  walls  are  lined  with  burnished  silver,  because  that 
metal  is  the  best  I'eflector  of  the  heat-rays ;  still,  brass  with 
a  light  coating  of  silver  would  also  serve  the  purpose.  The 
inclination  of  the  walls  of  the  apparatus  to  its  axis  measures 
45  deg.  Even  the  ancients  were  aware  that  this  is  the  best 
form  for  this  kind  of  metallic  mirrors  with  linear  focus, 
inasmuch  as  the  incident  rays  parallel  to  the  axis  are  reflected 
perpendicularly  to  the  same,  and  thus  give  a  focus  of  maxi- 
mum intensity. 

"The  boiler  is  of  copper,  which  of  all  the  common  metals 
is  the  best  conductor  of  heat ;    it  is  blackened    on  the  out- 


CUA1>.  XLV.  iiUy  I'OWEK-TUE  SOLAR  EXGIXE.  5C7 

side,  liecaiise  l)lack  possesses  tlie  property  of  absorbing  all 
the  heat-rays,  just  as  white  reflects  them;  and  it  is  enclosed 
in  a  glass  envelope,  ghvss  being  ilie  most  diathermanous  of 
all  bodies— that  is  to  say,  the  most  permeable  by  the  rays  of 
liiniinous  heat.  Glass  further  possesses  the  property  of  resist- 
ing the  exit  of  these  same  rays  after  they  have  been  trans- 
formed into  dark  rays  on  the  blackened  surface  of  the 
boiler.  None  of  the.se  applications  of  physical  laws  present 
any  novelty ;  people  induced  them  to  practice  instinctively, 
as  it  were,  before  men  of  science  could  assign  the  reasons. 
Here  the  arts  of  cookery  and  of  gardening,  and  the  pro- 
cesses for  warming  our  rooms,  did  uot  wait  for  the  experi- 
ments of  the  physicist.  Saussure  himself  started  from  these 
data  in  his  researches  ;  but  the  inventor  needed  the  discoveries 
of  modern  physics  in  order  to  give  to  these  applications  a 
ligorous  formula. 

"The  boiler  proper  of  the  Tours  solar  engine  consists  of 
two  concentric  bells  of  copper,  the  larger  one,  which  alone 
is  visible,  having  the  same  height  as  the  mirror — i.e.,  eighty 
centimetres— and  the  smaller  or  inner  one  fifty  centimetres; 
their  re,spective  diameters  are  twenty-eight  and  twenty-two 
centimetres.  The  thickness  of  the  metal  is  only  three  mil- 
limetres. The  feed-water  lies  between  the  two  envelopes, 
forming  an  annular  envelope  three  centimetres  in  thickness. 
Thus  the  volume  -of  li.piid  is  twenty  litres,  and  the  steam- 
chamber  hits  a  capacity  of  ten  litres.  The  inner  envelope 
is  empty.  Into  it  pass  the  steam-pipe  and  the  feed-pipe 
of  the  boiler.     To  the  sleamjiipe  are  attache<l  the  gauge  and 


568  SUN  POWER— THE  SOLAB  ENGINE.  chap.  xlv. 

the  safetj"- valve.  The  bell-glass  covering  the  boiler  is  eighty- 
five  centimetres  higli,  forty  centimetres  in  diameter,  and  five 
millimetres  in  thickness.  There  is  everywhere  a  space  of 
five  centimetres  between  its  walls  and  those  of  the  boiler, 
and  this  space  is  filled  with  a  layer  of  very  hot  air. 

"The  earth,  owing  to  its  diurnal  and  annual  revolution, 
does  not  occupy  the  same  position  with  regard  to  the  sun 
at  all  hours  of  the  day,  or  in  all  seasons  of  the  year.  This 
being  the  case,  the  generator  is  so  contrived  as  to  revolve 
15  deg.,  or  one  twenty-fourth  of  its  circumference,  hourly 
around  an  axis  parallel  to  the  earth's  axis — i.e.,  so  as  to 
follow  the  ajjparent  diurnal  motion  of  the  sun,  and  to  incline 
gradually  on  its  axis  in  proportion  to  the  solar  declination. 
Hence  the  intensity  of  the  utilized  heat  is  always  nearly 
the  same,  whatever  the  hour  of  the  day  or  the  season  of 
the  year,  inasmuch  as  the  apparatus  is  always  so  ari-anged 
as  to  reflect  with  the  least  possible  loss  all  the  rays  emitted 
by  the  sun.  This  double  motion  of  the  generator  is  effected 
by  a  very  simple  contrivance." 

The  foregoing  description  of  the  Solar  Steam-Generator 
of  Mouchot  is  so  lucid  that  it  requires  no  explanation.  Mr. 
Simonin,  however,  erroneously  supposes  that  the  power  de- 
veloped by  the  appai-atus  is  neaidy  the  same  at  all  hours  of 
the  day,  the  fact  being  that  the  energy  developed  by  the 
concentrated  solar  heat  varies  with  the  depth  of  atmosphere 
penetrated  by  the  rays.  The  latter  evidently  depends  on 
the  sun's  zenith  distance ;  hence  at  Paris,  where  the  maxi- 
mum   solar    intensity   during    the    summer    solstice    is    65°.0 


cuAP.  xLv.        su.\  rowEn—TUJi:  solaj:  EyaixE.  669 

Fall,  at  iiouu  (see  diagram  on  Plate  9),  it  .scarcely  reaches 
52°.0  F.  at  five  o'clock  in  the  afternoon,  owing  to  the  in- 
creased zenith  distance,  and  consequent  increase  of  the  depth 
of  atmosphere  to  be  penetrated  by  the  sun's  rays.  Obviously, 
the  efficiency  of  the  solar  generator  will  be  diminished  in 
the  same  ratio  as  the  stated  intensities.  Mr.  Simonin  states 
that  on  some  occjisions,  when  the  sun  has  been  exceptionally 
clear,  the  solar  generator  at  Tours  has  evaporated  five  litres 
of  water  per  hour,  which  he  assumes  equivalent  to  half  a 
horse-powei'.  The  reflector  producing  this  result — a  trun- 
cated cone — being  2.6  metres  (8  feet  6  inches)  in  diameter, 
it  will  be  found  that  in  order  to  double  the  reflective  area 
necessary  to  generate  steam  for  an  engine  of  one  horse-power, 
a  truncated  cone  of  3.(?  metres  (11  feet  9  inches)  aperture 
will  be  requii-ed.  Practical  engineei-s  are  aware  that  an 
inverted  conical  body  whose  base  is  nearly  12  feet  in  dia- 
meter, swinging  round  an  inclined  axle  at  least  60  deg.  on 
each  side  of  the  vertical  line,  presents  a  structure  so  for- 
midal)le,  even  if  counterpoised,  that  it  would  not  be  pradent 
to  increase  its  size.  Accordingly,  one  hundred  of  Mouchot's 
solar  generatoi*s  w-ould  be  needed  to  furnish  steam  for  an 
engine  of  100  horse — a  very  moderate  power,  if  employed 
for  manufacturing  or  other  industrial  purposes.  Referring  to 
the  diagram  on  page  ~^^^D,  Fig.  2,  representing  a  bird's-eye 
view  of  the  aperture  of  the  conical  reflector  at  Tours  in 
three  different  positions — viz.,  a  in  the  morning,  h  at  mid- 
day, and  c  during  the  afternoon — it  will  be  seen  that  each 
instrument,  owing   to   the   necessary  change  of  position,  de- 


570  SUN  PqWER-THE  SOLAB  ENGINE.  CHAP.  XLV. 

mjinds  a  front  sptice  of  nearly  twenty  feet.  If  placed  side 
by  side,  the  conical  solar  generators  required  for  an  engine 
of  100  horse-power  would  therefore  occupy  a  front  of  2,000 
feet  from  east  to  west.  If  arranged  in  four  lines,  with  suf- 
ficient s^iace  north  and  south  to  prevent  interference,  a  dis- 
tance of  500  feet  by  200  feet  would  be  required. 

Now,  let  us  consider  that  the  scheme  calls  for  100  sepa- 
rate boilers,  to  be  continually  fed  with  water,  the  height  of 
which  can  only  be  known  by  the  indication  of  outside  gauges, 
while  the  steam  from  the  scattered  boilers  must  be  conveyed 
by  a  series  of  flexible  tubes  to  the  motive  engine.  The  hun- 
dred glass  bells  can,  no  doubt,  be  dusted  and  kept  clean  with 
moderate  exertion ;  but  the  hundred  silver-plated  reflectors, 
which  Mr.  Simouin  says  must  be  exposed  to  the  vicissitudes 
of  the  atmosphere,  cannot  ,be  kept  bright  without  herculean 
labor,  since  silver  tarnishes  in  a  few  hours.  In  view  of  the 
foregoing  statement,  which  embraces  only  the  chief  difliculties 
attending  Mouchot's  system,  the  most  sanguine  might  well  de- 
spair of  rendering  sun-power  available  for  practical  pui-poses. 

The  Professor  of  the  Lycee  of  Alenyon,  in  claiming  to 
have  anticipated  me,  has  done  so  ignorant  of  the  fact  that 
sun-power  has  been  the  study  of  my  whole  professional  life 
— a  life  the  early  part  of  Avhich  was  chiefly  devoted  to  the 
production  of  a  cheaper  motive  power  than  steam.  The  in- 
dustrious scientist,  if  he  had  been  correctly  informed  on  the 
subject,  would  no  doubt  have  perceived  the  advantages  re- 
sulting from  such  antecedents,  with  reference  to  a  successful 
practical  solution  of  the  problem  of  utilizing  solar  heat. 


CHAP.  xLv.        srx  rowEn-rnE  solar  exoine.  571 

On  grounds  already  fully  explained,  minute  plans  of  my 
new  system  of  rendering  sun-power  available  for  mecbanioal 
purposes  will  not  be  presented  in  this  work.  The  occasion, 
however,  demands  that  I  should  present  an  outline  of  the  cm- 
centration  apparatus  befoi'e  referred  to.  It  consists  of  a  series 
of  polished  parabolic  troughs,  in  combiinitioii  with  a  system 
of  metallic  tubes  charged  with  water  under  pre.ssure,  e.vposed 
to  the  influence  of  converging  solar  rays,  the  augmented  mole- 
cular action  produced  by  the  concentration  being  transferred 
to  a  central  receiver,  from  which  the  accunuilated  energy  is 
communicated  to  a  single  motor.  Thus  the  mechanical  power 
developed  by  concentrated  solar  heat  is  imparted  to  the  solar 
steam-engine  without  the  intervention  of  a  multitude  of  boilere, 
glass  bells,  gauges,  feeders,  etc.  Moreover,  the  concentration 
apparatus,  unlike  the  instrument  of  Mouchot,  requires  no 
parallactic  motion,  nor  does  its  management  call  for  any 
knowledge  of  the  sun's  declination  from  day  to  day.  Its 
jwsition  is  regulated  by  simply  turning  a  handle,  until  a 
cei-tain  index  coincides  with  a  certain  bright  line  produced 
by  the  reflection  of  the  sun's  rays. 

Plate  07  represents  a  perspective  view  of  a  solar  engine, 
in  which  the  concentrated  energy  of  the  sun's  rays  is  com- 
municated to  the  motor  by  means  of  heated  atmospheric  air, 
instead  of  being  communicated  l)y  water  heated  under  pres- 
.sure  and  expanded  into  steam.  A  glance  at  the  illustration 
shows  that  the  upper  end  of  the  working-cylin<ler  is  heated 
by  the  sun's  rays  reflected  by  a  curved  mirror.  It  will  be 
seen  by  carefid  examination  that  the  solar  rays  converge  at 


672  SUN  PO  WEE-TEE  SOLAR  ENGINE.  CHAP.  XLV. 

a  point  beyond  the  axis  of  the  reflector;  heuce  tliat  the 
form  of  the  latter  is  not  parabolic,  but  composed  of  an 
irregular  curve.  The  object  is  that  of  spreading  the  con- 
verging rays  over  a  greater  length  of  the  cylinder  than 
possible  with  the  divergence  which  would  result  from  em- 
ploying a  reflector  of  true  parabolic  curvature.     It  will   be 


perceived  on  insi^ection  that  the  upper  end  of  the  cylinder 
will  be  subjected  to  a  concentration  of  heat  many  times 
greater  than  the  concentration  at  the  lower  end.  Referring 
to  the  accompanying  diagram  representing  a  vertical  section, 
of  the  machine,  it  will  be  seen  that  the  working-cylinder, 
open  at  the  lower  end,  contains  two  pistons,  a  working- 
piston  a  and   an   exchange-piston  b.     The  working-piston   is 


CHAP.  XLV.  SUX  rOWEU—TUE  SOLAR  ENGINE.  573 

CDiuiected  with  tlio  crank-shaft  d  by  the  beam  c  and  the 
connecting-rod  </.  The  exchange-piston  Z>  is  connected  witli 
the  crank-shaft  by  the  bell-ci-aiik  //  and  connecting-rod  //. 
An  annular  space  is  formed  round  tlie  excliange-piston, 
admitting  of  a  free  passage  of  the  air  from  end  to  end  of 
the  cylinder  during  the  motion  of  this  piston.  It  will  l;e 
readily  understood  that  during  the  downward  motion  of  the 
exchange-piston  the  cold  air  from  the  lower  end  of  the 
cylinder  will  be  transferred  to  the  upper  end,  heated  by 
the  concentrated  solar  rays ;  lience  internal  pressure  will  be 
produced  tending  to  force  the  working-piston  down.  By  a 
careful  examination  of  the  combination  of  the  several  work- 
ing parts,  it  will  be  easily  comprehended  how  the  working- 
piston  is  actuated  by  the  confined  air,  heated  and  cooled 
alternately  by  the  peculiar  motion  of  the  exchange-piston. 
It  will  be  evident  that  the  large  surface  presented  by  the 
outside  of  the  exchange-piston,  and  inside  of  the  cylinder, 
•will  cause  a  rapid  change  of  temperature  of  the  air  while 
circulating  from  end  to  end  of  the  latter.  The  upper  end 
of  the  cylinder  being  heated  by  the  concentrated  solar 
rays,  the  cold  air  from  the  lower  end  \n\\,  during  its  trans- 
fer to  the  upper  end  caused  by  the  downward  motion  of 
the  exchange-piston,  become  heated  and  expanded;  while 
during  the  upward  motion  of  the  .said  piston  the  air,  in 
being  transferred  to  the  lower  end  of  the  cylinder,  becomes 
cooled  and  contracted.  It  will  be  found  on  due  considera- 
tion that  the  exchange-piston  thus  performs  the  office  of  a 
regetierator.     The    engine,   therefore,   is  capable    of   ojieiating 


574  SUN  rOWEB-THE  SOLAR  ENGINE.  chap.  xlv. 

for  a  considerable  time  by  exposing  tlie  upper  end  of  the 
cylinder  to  the  reflected  solar  heat  during  a  few  minutes  at 
starting.  By  continuous  exposure  to  the  concentrated  solar 
rays,  the  engine  performs  fully  400  turns  per  minute.  It 
should  be  observed  that  concentrated  solar  radiation  supplies 
heat  with  such  extraordinary  rapidity  that  the  apparently 
insufficient  amount  of  heating  surface  presented  by  the 
cylinder  has  proved  adequate,  notwithstanding  the  great 
speed  of  the  engine.  It  only  remains  to  be  stated  that  the 
body  fii  m  represents  a  radiator  carrying  off  the  heat  which 
is  not  taken  up  by  the  circulating  air  during  the  motion  of 
the  exchange-piston.  Of  course,  the  amount  of  heat  carried 
off  by  the  radiator  furnishes  a  nearly  correct  measure  of  the 
solar  energy  not  converted  into  mechanical  work.  Engineers 
need  not  be  reminded  that  the  form  of  the  solar  engine  thus 
described  is  applicable  only  for  purposes  requiring  moderate 
power.  In  the  largest  class  of  solar  engines  actuated  by 
atmospheric  air,  in  which  the  radiator  is  incapable  of  ab- 
stracting the  sujierfluous  heat,  I  employ  valves,  and  take  in 
fresh  air  at  each  stroke  of  the  machine,  precisely  as  in  the 
caloric  engine  delineated  on  Plate  46. 

Having  thus  cursorily  examined  the  construction  of  the 
solar  engine  actuated  by  the  intervention  of  atmospheric 
air,  and  briefly  adverted  to  the  steam  solar  engine  and  the 
mode  adopted  in  concentrating  the  molecular  motion  im- 
parted by  solar  radiation,  and  also  pointed  out  the  nature 
of  the  expedient  resorted  to  in  transferring  the  said  con- 
centrated molecular  motion  to  mechanical  motors,  let  us  now 


CHAP.  XLV.  SUN  roWEli-TUE  SOLAIi  AWGIXE.  575 

consider  the  stupfiulous  amount  of  the  energy  at  our  com- 
mand. 

It  has  already  been  stated  that  the  result  of  repeate.l 
e.\i)eriments  with  the  concentration  a^iparatus  shows  that  it 
abstracts  on  an  average,  during  nine  hours  a  da}-,  for  all 
latitudes  between  the  equator  and  45  deg.,  fully  :].'»  units 
of  heat  per  minute  for  each  sipiare  foot  of  area  presented 
perpendicularly  to  the  sun's  rays.  Theoretically,  this  indi- 
cates the  development  of  an  energy  etpial  to  8.2  horse- 
power for  an  area  of  100  square  feet.  On  grounds  before 
explained,  our  calculations  of  the  capabilities  of  sun  power 
to  actuate  machinery  will,  however,  be  based  on  one  horse- 
power developed  for  loo  s(puire  feet  e.\-i)osed  to  solar  radia- 
tion. The  isolated  districts  of  the  earth's  surface  suffering 
from  an  excess  of  solar  heat  being  very  numerous,  our  space 
only  admits  of  a  glance  at  the  sunbui-nt  continents. 

There  is  a  rainless  region  extending  from  the  northwest 
coast  of  Afi-ica  to  Mongolia,  9,000  miles  in  length  and  nearly 
1,000  miles  wide.  Besides  the  North  Afiican  deserts,  this  re- 
gion includes  the  southern  coast  of  the  Mediten-anean  east  of 
the  Gulf  of  Cabes,  Upper  Egypt,  the  eastern  and  i)art  of  the 
western  coast  of  the  Eed  Sea,  part  of  Sp-ia,  the  eastern  part 
of  the  countries  watered  l)y  the  Euphrates  and  Tigris,  Eastern 
Arabia,  the  greater  pait  of  Persia,  the  extreme  western  part  of 
China,  Tibet,  and,  lastly,  Mongolia.  In  the  western  hemisphei-e. 
Lower  California,  the  table-land  of  Mexico  and  Guatemala, 
and  the  west  coast  of  South  America,  for  a  distance  of  more 
than  2,000  miles,  suffer  from  continuous  intense  radiant  heat. 


5rG  Sm'  rOWFAt—THE  SOLAR  ENGINE.  chap.  XLV. 

Computations  of  tlie  solar  energy  wasted  on  the  vast 
areas  tlius  specified  would  present  an  inconceiva1)ly  great 
amount  of  dynamic  force.  Let  us,  therefore,  merely  esti- 
mate the  mechanical  power  that  would  result  from  utilizing 
the  solar  heat  on  a  strip  of  land  a  single  mile  in  width,  along 
the  rainless  western  coast  of  America ;  the  southern  coast  of 
the  Mediterranean  before  alluded  to ;  both  sides  of  the  allu- 
vial plain  of  the  Nile  in  Upper  Egypt;  both  sides  of  the 
Euphrates  and  Tigris  for  a  distance  of  400  miles  above  the 
Persian  Gulf ;  and,  finally,  a  strip  one  mile  wide  along  the 
rainless  portions  of  the  shores  of  the  Red  Sea,  before  pointed 
out.  The  aggregate  length  of  these  strips  of  land,  selected 
on  account  of  being  accessible  by  water  communication,  far 
exceeds  8,000  miles.  Adopting  the  stated  length  and  a 
■width  of  one  mile  as  a  basis  for  computation,  it  will  be  seen 
that  this  very  narrow  belt  covers  223,000  millions  of  square 
feet.  Dividing  the  latter  amount  by  the  area  of  100  square 
feet  necessary  to  produce  one  horse-power,  we  learn  that 
22,300,000  solar  engines,  each  of  100  horse-power,  could  be 
kept  in  constant  operation,  nine  hours  a  day,  by  utilizing 
only  that  heat  which  is  now  wasted  on  the  assumed  small 
fraction   of  land   extendiuof  alonsf    some   of   the    water-fronts 

o  o 

of  the  sunburnt  regions  of  the  earth.  Due  consideration 
cannot  fail  to  convince  i:s  that  the  rapid  exhaustion  of  the 
European  coal-fields  will  soon  cause  great  changes  with 
reference  to  international  relations,  in  favor  of  those  coun- 
tries which  are  in  possession  of  continuous  sun-power. 
Upper  Egypt,  for  instance,  will,  in  the  course  of  a  few  cen- 


CHAP.  XLV.  SUN  POWEU-THE  SOLAU  ENGINE.  577 

turies,  derive  signal  advantage  and  attain  a  liigli  i.ditiial 
position  on  account  of  her  iierpetual  suiisliinc  and  the  eon- 
sequent  command  of  unlimited  motive  force.  The  time  will 
come  when  Europe  nuist  stop  her  mills  for  want  of  coal. 
Upper  Egypt,  then,  with  her  never-ceasing  sun-power,  will 
invite  the  European  manufacturer  to  remove  his  machiueiy 
and  erect  his  mills  on  the  firm  ground  along  the  sides  of 
the  alluvial  plain  of  the  Nile,  where  an  amount  of  motive 
power  may  be  ol)tained  many  times  greatei'  than  that  now 
employed  by  all  the  manufactories  of  Europe. 


V 


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Flate  1.     Hee  (Juaf.  I. 


Instkument  fok  measuring  the  Ixtexsity  of  Radiation  from 

Enclosed  Concave  IlAniATous. 

Designed  hy  .Toiix  Ekicsson.     Manufactured  at  New  York,  1873. 


Plate  2.    See  Chap.  I. 


DiAouAMS  snoTviNo  THE  Propaoatiox  of  Radiant 
Heat  tiiikiuoii  Space. 


Plate  3.     Se£  Chap.  I. 


Instrument  suowing  the  Rate  ob^  Cooling  of  a  Ueated  Body 

wiTiiix  AN  Exhausted  Cold  Enclosuue. 

Desiuxed  hy  John  Ericsson.     Manufactured  at  ^i'ew  York,  i8?a. 


ym.  I 


Plats  4.    See  Chap.  11. 


IXSTKI'MKNT    SHOWIXU    TIIK    HaTE    <iK    IIlOATI.NCi    OF    A    CoLl)    linUV 
WmilX    AN    KXIIAISTKI)     IIeATKU    EXCLOSUlUi. 

Dksicnkd  1!Y  John  Euicssox.     Manifactiuku  at  Ni;\v  Youk,  ist-l 


FLATK  5.      i)££   CUAi:    II. 


IXSTKFMENT  SnOWINO  TITE   RaTE  OF  COOLINO  OF  AN  IXCAXDESCEXT 

Sphere  within  an  Exhausted  Cold  Encloscue. 
"Desioned  i?y  Johx  Eimosson.     Manufactured  at  New  Yoi:k,  1874. 


^}K^ 


Plate  G.     See  Chap.  II. 


I    3 

5.      > 

en 

o      w 

^  i 

53  S 


2       B 


Plate  7.     Skf.  Ciiav.  II. 


ACTINOMETEU,  FOR   MEASURING  THE   INTENSITY   OF   SoLAU  RaDIATIOX. 

Designed  by  John  Ericsson.     MANriACTrnnn  at  Xkw  Yoi:k,  i870. 


Pr.ATk  8.     See  Vuap.  HI. 


Plate  9.     See  Cuav.  III. 


Solar  Calokimetkr,  i-ou  MEAsrniNc;  tiik  Meciia.vical  Enekoy  ok 

Solar  IlAniATiox.     Designed  hy  Joii.v  Ericssox. 

Manufactured  at  New  York,  i870. 


Plate  10.     See  Chap.   V. 


PoKTAiii.K  SoLAK  Cai.()i:imktki:.  kok  MKAsui:i.\(i  Tin;  Mechanical  Enki!oy 

<>I'    SoLAi:    ItADIAlloV.       l)i:si(;XKI>    ItY    .lollX    ElMCSSON. 
MaM1A(  TIIMM)    AT    XkW     Y(I1;K,    1N74. 


PI.ATE  11.     See  Chap.   V. 


l)iA(;i:.vMs  siiowiNd  tiik  JIaihatiox  fkom  Dikkkkknt  Parts 
(IK  TKE  Soi.Aij  Disc. 


Plate  12.     See  Chap.  VI. 


PAl^ALLACTIc  Mechanism  fou  mkasukixg  tiik  Lvtensity  ok  RadiXtio.v 

FROAI   DiFFERKNT   PaKTS   OF  THE   SoLAR   Dl-Si'. 

Designed  uv  Joux  Euicssux.     Coxstkuctkd  at  New  Yokk,  18T5. 


Plats  13.     See  Cbap.   VI. 


DiAdu.vM  siiowiNd  Tin:  Attuactiox  witiiix  tiii-;  Solai:  Mass 
AT  I)ii'i-ki:i:n  r  Distaxcks  viu>m  its  Ckntuk. 


Plate  U-    See  Chap.   VII. 


iNSTTltTMENT   FOU   MKASURIXC,   TIIK   RaDIAXT  PoWER  OF   TIIK   SoLAR 

Atmosphere.     Designed  by  Jonx  Ericssox. 

MANTFArTCKED    AT   NkW    YoRK,   1873. 


Plate  15.    Skk  Cn.ir.   VIII. 


DiAiiUAMs  siiowixd  Tin;  ]{ai>ia.nt  Puwkk  111-  Till-; 
SoLAU  Atmospiikkk. 


Plate  16.     See  Cuai>.    VI 11. 


LnSTKUMENT    Full    MEASUKI.NG    TilK    AClLAJ.    INTENSITY    OF   TllK   Sux's    RaY: 

Designed  uv  John  Ekicsson.     Maxufactueed  at  New  Yokk.  isn. 


Flate  17.     i>£i:  CuAP.  IX. 


Instrhment  for  showin'g  the  Fkebleness  of  Solai:  Radiation-. 
Desic.xkp  itY  Joiix  Ericssox.    Coxstructed  at  Xkw  York,  isn. 


Plate  la.     .Sav;  (  iiai:  1.\. 


SOLiVIi    PVKOMETKU,    FOU    ASCERTAIXIXO    THK   TKMPICnATrKI':    OF   TIIF, 
SOLAU   SCKFACE.      DESIGNED    BY   JoiIX    ElilCSSON. 

Constructed  at  New  York,  isto. 


Pr.ATK  10.     See  ('iiaf.  X. 


Appaijatus  fok  MKAsiuiixG  THE  IIauiant  Intensity  ok  Flames. 
Designed  by  John  Eiucsson.     Constkuoted  at  New  York,  is71. 


FIG.  9 


Platb  20.    Hee  ViiAP.  X 


INSTKUMKNT   FOU    MKA.SUKIXG    THE    UaDIATIOX    l-llU.M    IXCAXDESCEXT 

Planes.     Designed  by  John  Ericsson. 
Manufactuued  at  New  Youk,  18?^. 


Plate  21.     !See  C'jjaj:  XL 


DlAfiUA.MS    SlIOWIXO    TIIK   RaDIATIOX    AT    DIFFERENT    INCLINATIONS 

OF  Incandescent  Planes. 


Plate  22.      See  Cum:  XL 


IXSTUrAfKXT    KOU    MKASI'IUXC.    TUr.    UvniATIOX    VUOM    DUKKKKXT    ZOXKS 

OF  Incandkscent  Spheres.     Dksioxkd  hy  Joiix  Ekicssox. 
Manufactured  at  New  York,  i8?3. 


Pr,ATK  2.J.     See  C'//.tr.   XI I. 


DiAtSUAMS    SHOWINti    THK    RaDIATIOX    KUoM    DlKKKKKNT    ZoNKS 

OF  Incandksoent  Spiieues. 


Plate  24.     See  Cuai:  A'II. 


OaLOKIMETEK,    KOK   MEASL'lUNti    THE  ENKKliV    DKVELUPED    »Y    R.VDIATIOX 

OK  FusKD  luoN.     Desujneu  hy  Joux  Ekicsson. 

CONSTRUOTEU    AT   NeW    YultK,    1B?J. 


Ov 


/'.>/ 


Plate  ^o.     See  Vuaj:  All  I. 


AppAUATrs  Koi:  mkasiimm;   IIakiant  IIkat  iiy  mkans  uk  tiik   Tiikkmo- 
Elkctrio  PiLK.     Dksiuxk.i)  hy  John'  Kuicssox. 

CONSTIMTTKU    AT    XkW    Y<iKK,    lrtT4. 


Pl.iti-:  .'>J.     ShK  (  IIAI-.  .\  I  \ 


B.VlIoMr.TKIC    ACTIVOMKTKI:,     von    MKASintINt!    TIIK    IXTKN'SITV    OK 

SoLAK  1{ai)[aiion.     l)i:si(i\Ki)  HY  .loiix  Ericsson. 
MANtrKArrruKn  at  Nkw   Vokk,  1874. 


PrMTK  27.     Skf  r/fAP.  ATI. 


!25 


M 

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r> 

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Flate  ^S.     ,SA'i'  C'//.ii'.  A' 1 7/. 


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53 

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o 

K 

Pijrs  ;?5.     S£E  CuAi:  X  VIII. 


Instrument  for  measuring  the  Reflective  Power  of  Silver  and 

OTHER  Metals.    Designed  by  John  Ericsson. 

Manufactured  at  New  York,  1874. 


FIG.  I 


FIG.  2. 


Vi. 


Plate  30.     See  Ciiap.  XIX. 


Rapid-In'dkwtiox  Actinometer,  for  ME.vsrRixo  THE  Intensity  of 

Solar  Radiation.     Designed  by  John  Ericsson. 

Manufactured  at  New  York,  18T3. 


Plate  31.     See  Chap.  XX. 


ApPAKATUS    I'OK    ASCKKTAINING    TlIK    DlATUKlUIANCV    OF    Fl^JIKS. 

Designed  by  Joun  Ericsson.    Constructed  at  New  York,  1872. 


Plate  32.     Sek  Cuap.  XXI. 


DiACiKAM    KKIMIESENTING   A   SECTION    (»I'   TllK   EaKTH    AXD 
CERTAIN    RiVEU    BaSINS. 


Plate  33.     :^£E  Cu.u:  A' A 11. 


Byxamic  Rkcistkh  I'on  mkasi-kixc  tiik  Uki.ativk  Pdwku  oi'  CruitKXT? 

OF  NVatku  and  Vai'oi:.     Dksioned  ]?y  .Tohx  Eutcssox. 

Manukactithkh  at  Nkw  York,  1871. 


I'LATE  04.    Hee  Cj/aj:  XXII. 


T)i\(;n.\:Nt  snowixr,  the  Result  of  Experiments  with  tiik 
Dynamic  Rec.i^jtkr. 


Plate  J'j.    Ske  Ciiai:  A' A  J  I. 


DiSTANTK  Insi  i;r.MK.\T  Kui;  mi;asiui.\(;  DisTANcKs  AT  Sea. 
DissiGNEi)  i!v  ilt'iiN  Ki;icss().\.     Manufactl'iu:u  at  Nkw  YoUK,  l»4l. 


Plate  jo.    Hes  Cuai:  A'AJJI. 


Steam  Fire-Engine.    Designed  by  Jouji  Ericsson',  1841. 


Plate  87.    See  Chap.  A'A'IV. 


H 

5? 

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55 

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Plate  3S.    See  Ciiaf.  XXV 


5<         c 


Plate  39,     See  Chap.  XXV. 


< 


c      S 

K         O 
CQ 

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T'A.iT-i;  ^0.     6'£A-  (7/.I/'.  XXK. 


pLATt:  J,l.     iSEE  CuAi:  AAV  I. 


./.        ^_^ 


Vlate  \2.     St:i:  Cum:   .WVIII. 


SlTRFACK-CoNnENSKU.       ]  )KSI<;NKr)    AND    PaTKXTKI)    IIV    .TolIN    EuiCSSON,    1849. 
lUILT    AT    NKW    Vi>i:K. 


Pi.ATK  Jt3.     See  Cum-.  XXIX. 


EXI'KKIMKNTAL    CaLuKIC    ExUINK.       DksIUXKU    ItV    .lollN    ElMCSSON. 

BlILT    AT    JsKW    YuUK,     18-jI. 

TUAXSVKUSK   SKCTIUX. 


Pl.itic  44-     ''•^i^-'^'  tUAf.  XXX. 


rt 


M 


5    Z 

2    '-^ 


c       B 


K 


Plate  Jto.     See  Cuap.  AJ:'X 


Oai.oiik-  Km;ini'.  pdi:  Domkstic  Pi'im'osks.      DiwiuNKn  nv  John  Eimcssox. 
Biii.T  IN  Amkkica  and  Eiiiori',  mui.Mi  a  Skuiks  of  Vkaks. 

LOXCinriJlNAI.    SKClldN. 


Pi^ATK  40.     ShK  Cum:  .\'.\'.\7. 


TiiK  '•  MiiMToi:."     T)i:si(;\i:i)  isv  .loiix  Ei;ic»suN.     Biilt  at  ]S'i;\v  Y(ii:k,   isui. 


niXK   PLAN. 


TnAx=;vER'!K  '^T.rTiny  nv  Tiri.L  and  rrnnET. 


PhATF:  1,7.     Ske  Cum:  XXA'll. 


s 


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Q 

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!z) 


o 

w 
PI 


Plate  A8.     Sek  Chap.  XXXII. 


MoNiTou  OK  Tinc  "Passaic"  Class.    Designkd  hy  John  Eijicsson. 
Ten  Monitoks  of  this  Class  hiilt  at  Nk.w  Youk  and  otmku  Places. 


SIDE    ELEVATION. 


TKANSVEKSE  SECTION  OF  TUUKET   AND   PILOT-HOUSE. 


Plate  49.     See  Chap.  XXX 111. 


y 

'y. 

n 

7: 

a 

y 

M 

o 

C3 

t/j 

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:/j 

►^ 

Plate  hi).     See  Cuav.  XXXIV. 


td 


tj      "^ 


w 
o 

^      S      ^^ 

S      S      15 
^       d 

o 


Pi.ATK  ■'>!.     Si:k  fiiAi:  XXXIW 


J 


MoxiTou  ••  Dr-iat(ii:."     Dksiuxkd  uv  John  Eiucsson. 
EuiLT  AX  New  York,  1862. 


SIDE  ELEVATION. 


DECK  PLAN. 


LENGTH  ON  DECK,  312  FEET.      BEAM,  50  FEET.      DEPTH,  21  FEET  6  INCHES. 

STEAM-CYLINDERS,  100  INCHES  DIAMETER,  4  FEET  STROKE. 

PROPELLER,  31  FEET  6  INCHES  DIAMETER. 


I'LATt:  J  J.     SEt:  LuAP.  XXXV. 


S 

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ili;i.i,.,         .lii 


Plate  53.     Sjce  Cuai'.  XXXV. 


2        " 


Plate  5^.     See  Cuai:  XXXV 


Pr.ATE  '>',.     Skk  CiiAi:  A' A' AT 


w      ^ 


3      ^ 


3      / 


,-£] 


Zl 


m 


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M  S 


3       1-3 


J'latk  jo.     Sfn  L'UAF.  A'XA'17. 


Cakuiages  fou  Hkavy  Ordxaxck.    Designkd  by  John  Ericsson,  i8Gi. 

section  showing  the  kkictiox-geak  ai'l'lied  to  the  gun-cakkiages 
oe  the  united  states  uton-clau  fleet. 


SECTION   SHOWING   CAPTAIN'   SCOTT  S    I'LACil AltlSM. 


SECTION   SHOWING   SIi:    WILLIAM    AKMSTKONG  S   PLAGIARISM. 


PLATt:  o7.     St:t:  VuAi:   XXWll. 


w 


Plate  .IS.     Sek  Ciiai;  XXXVIJL 


w 

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2      2 


Pi.ATh:  .Vi.     Skk  Cii.ii:   .VA'A'JS. 


O 

a 

C>1 


pLATi;  (Jij.     Hke  CuAi:  XL, 


TllK    SrANISII    GUNliOAT   ExcilNKS.       DESUiXKK    HY    .lollX    ElUCSSON. 

Built  at  Nkw  Yoiik,  18G9. 


PhATK  01.     .s>.>;  CiiAi:  XLI. 


illSHIlllli 


'I 


iw 


Mh 


Nl 


I 


K^Wi 


Platk  OJ.     Si:k  iii.u:   Xl.ll. 


^^^)VATiI.K  Torpedo.     Bestgnkd  isv  John  Eiircssox.     Bt'ilt  at  Nkw  Yokk,  187:!. 


I'l.ATH  0-1.     Skk  Cum:   XI.lll, 


AlU-CoMPRESSOlt,   FOll  TIIK   TuAXSMISSIOX    OK   MkCMANICAL   PoWKU 

Designed  by  Joiix  Ericsson.     Built  at  New  Youk,  I8;a. 

PERSPECTIVE   VIKW. 


Plate  0'4.     tii:^  Ciiai:  ALU'. 


^ 


AiR-CoMPincssoi!,  Kou  TiiK  Tkaxsmissiox  of  Mechanical  Puwkk 
Designed  by  John  Ericsson.     Built  at  New  York,  1873. 
transverse  section. 


Platk  65.     See  Ouai'.  XLIV. 


^>f^ 


a      ^ 


o 


Pi^r^  C6.     6'£'£  C'i/.4i'.  XLV 


Solar  Exgine,  operated  by  the  Intervention  of  Atmospiierto  Am 
Designed  hy  John  Ericsson.     Built  at  New  York,  1872. 


Platk  67.     See  Chap.  XLV. 


//v^/^^^i  /*-■::>!  h 


/'.--(' 


r"^f  y, 


**^\!'^c«s,7  A.^'-; 


n:^':?«;/"%\;I,:;- 


->La:^^ 


^^^^■;■J'^c"^r^.r^^ 


\,^,^ 


\/^'  'W'w N'/r^^M /fcA/r  ' " 


^:aaa^^'/a;»^^^VR?^^/>'^^^  ^a?^^' 


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